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 $20.49   4.224%   $21.3555   $21.36   $21.35   $21.40  
  Purchase #2 $193.38   9.594%   $211.9329   $211.93   $211.95   $211.90  
  Purchase #3 $190.41   11.301%   $211.9282   $211.93   $211.95   $211.90  
  Purchase #4 $195.43   7.786%   $210.6462   $210.65   $210.65   $210.60  
  Purchase #5 $130.89   9.540%   $143.3769   $143.38   $143.40   $143.40  
  Purchase #6 $136.34   11.150%   $151.5419   $151.54   $151.55   $151.50  
  Purchase #7 $29.63   11.279%   $32.972   $32.97   $32.95   $33.00  
  7 purchase totals = $896.57       $983.7536   $983.76   $983.80   $983.70