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 $165.73   10.588%   $183.2775   $183.28   $183.30   $183.30  
  Purchase #2 $176.39   11.569%   $196.7966   $196.80   $196.80   $196.80  
  Purchase #3 $216.56   13.612%   $246.0381   $246.04   $246.05   $246.00  
  Purchase #4 $111.85   6.352%   $118.9547   $118.95   $118.95   $119.00  
  Purchase #5 $241.29   4.629%   $252.4593   $252.46   $252.45   $252.50  
  Purchase #6 $24.39   9.764%   $26.7714   $26.77   $26.75   $26.80  
  Purchase #7 $48.98   7.800%   $52.8004   $52.80   $52.80   $52.80  
  7 purchase totals = $985.19       $1,077.0980   $1,077.10   $1,077.10   $1,077.20