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 $46.97   8.520%   $50.9718   $50.97   $50.95   $51.00  
  Purchase #2 $94.74   10.215%   $104.4177   $104.42   $104.40   $104.40  
  Purchase #3 $154.93   6.744%   $165.3785   $165.38   $165.40   $165.40  
  Purchase #4 $121.38   7.789%   $130.8343   $130.83   $130.85   $130.80  
  Purchase #5 $110.95   10.491%   $122.5898   $122.59   $122.60   $122.60  
  Purchase #6 $41.87   4.791%   $43.876   $43.88   $43.90   $43.90  
  Purchase #7 $117.27   13.227%   $132.7813   $132.78   $132.80   $132.80  
  7 purchase totals = $688.11       $750.8494   $750.85   $750.90   $750.90