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 $111.63   13.692%   $126.9144   $126.91   $126.90   $126.90  
  Purchase #2 $186.99   6.490%   $199.1257   $199.13   $199.15   $199.10  
  Purchase #3 $215.80   11.187%   $239.9415   $239.94   $239.95   $239.90  
  Purchase #4 $65.39   11.121%   $72.662   $72.66   $72.65   $72.70  
  Purchase #5 $78.33   11.869%   $87.627   $87.63   $87.65   $87.60  
  Purchase #6 $231.98   13.767%   $263.9167   $263.92   $263.90   $263.90  
  Purchase #7 $191.40   13.722%   $217.6639   $217.66   $217.65   $217.70  
  7 purchase totals = $1,081.52       $1,207.8512   $1,207.85   $1,207.85   $1,207.80