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 $82.33   13.727%   $93.6314   $93.63   $93.65   $93.60  
  Purchase #2 $102.92   9.549%   $112.7478   $112.75   $112.75   $112.70  
  Purchase #3 $235.78   8.838%   $256.6182   $256.62   $256.60   $256.60  
  Purchase #4 $76.98   10.363%   $84.9574   $84.96   $84.95   $85.00  
  Purchase #5 $182.74   7.759%   $196.9188   $196.92   $196.90   $196.90  
  Purchase #6 $82.85   11.453%   $92.3388   $92.34   $92.35   $92.30  
  Purchase #7 $67.82   12.208%   $76.0995   $76.10   $76.10   $76.10  
  7 purchase totals = $831.42       $913.3119   $913.32   $913.30   $913.20