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 $67.76   6.190%   $71.9543   $71.95   $71.95   $72.00  
  Purchase #2 $223.99   3.767%   $232.4277   $232.43   $232.45   $232.40  
  Purchase #3 $213.69   10.824%   $236.8198   $236.82   $236.80   $236.80  
  Purchase #4 $104.90   11.692%   $117.1649   $117.16   $117.15   $117.20  
  Purchase #5 $65.65   5.174%   $69.0467   $69.05   $69.05   $69.00  
  Purchase #6 $20.37   6.195%   $21.6319   $21.63   $21.65   $21.60  
  Purchase #7 $135.47   13.376%   $153.5905   $153.59   $153.60   $153.60  
  7 purchase totals = $831.83       $902.6358   $902.63   $902.65   $902.60