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 $44.64   8.204%   $48.3023   $48.30   $48.30   $48.30  
  Purchase #2 $201.91   4.776%   $211.5532   $211.55   $211.55   $211.60  
  Purchase #3 $124.79   6.252%   $132.5919   $132.59   $132.60   $132.60  
  Purchase #4 $111.91   11.594%   $124.8848   $124.88   $124.90   $124.90  
  Purchase #5 $102.26   8.757%   $111.2149   $111.21   $111.20   $111.20  
  Purchase #6 $144.38   12.252%   $162.0694   $162.07   $162.05   $162.10  
  Purchase #7 $236.39   3.626%   $244.9615   $244.96   $244.95   $245.00  
  7 purchase totals = $966.28       $1,035.5780   $1,035.56   $1,035.55   $1,035.70