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 $112.38   3.172%   $115.9447   $115.94   $115.95   $115.90  
  Purchase #2 $44.87   3.754%   $46.5544   $46.55   $46.55   $46.60  
  Purchase #3 $55.26   9.759%   $60.6528   $60.65   $60.65   $60.70  
  Purchase #4 $167.95   8.677%   $182.523   $182.52   $182.50   $182.50  
  Purchase #5 $128.92   11.343%   $143.5434   $143.54   $143.55   $143.50  
  Purchase #6 $155.65   4.350%   $162.4208   $162.42   $162.40   $162.40  
  Purchase #7 $95.40   6.809%   $101.8958   $101.90   $101.90   $101.90  
  7 purchase totals = $760.43       $813.5349   $813.52   $813.50   $813.50