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 $125.56   8.452%   $136.1723   $136.17   $136.15   $136.20  
  Purchase #2 $139.25   11.452%   $155.1969   $155.20   $155.20   $155.20  
  Purchase #3 $58.77   13.406%   $66.6487   $66.65   $66.65   $66.60  
  Purchase #4 $24.86   11.312%   $27.6722   $27.67   $27.65   $27.70  
  Purchase #5 $141.53   8.650%   $153.7723   $153.77   $153.75   $153.80  
  Purchase #6 $212.35   8.195%   $229.7521   $229.75   $229.75   $229.80  
  Purchase #7 $144.55   8.701%   $157.1273   $157.13   $157.15   $157.10  
  7 purchase totals = $846.87       $926.3418   $926.34   $926.30   $926.40