Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $108.42   10.432%   $119.7304   $119.73   $119.75   $119.70  
  Purchase #2 $158.62   12.172%   $177.9272   $177.93   $177.95   $177.90  
  Purchase #3 $165.46   5.649%   $174.8068   $174.81   $174.80   $174.80  
  Purchase #4 $247.32   13.588%   $280.9258   $280.93   $280.95   $280.90  
  Purchase #5 $217.30   4.294%   $226.6309   $226.63   $226.65   $226.60  
  Purchase #6 $118.67   7.495%   $127.5643   $127.56   $127.55   $127.60  
  Purchase #7 $219.92   11.561%   $245.345   $245.35   $245.35   $245.30  
  7 purchase totals = $1,235.71       $1,352.9304   $1,352.94   $1,353.00   $1,352.80