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 $114.48   4.388%   $119.5034   $119.50   $119.50   $119.50  
  Purchase #2 $133.67   9.429%   $146.2737   $146.27   $146.25   $146.30  
  Purchase #3 $87.98   5.203%   $92.5576   $92.56   $92.55   $92.60  
  Purchase #4 $54.88   4.825%   $57.528   $57.53   $57.55   $57.50  
  Purchase #5 $19.89   3.184%   $20.5233   $20.52   $20.50   $20.50  
  Purchase #6 $175.82   11.123%   $195.3765   $195.38   $195.40   $195.40  
  Purchase #7 $236.72   5.156%   $248.9253   $248.93   $248.95   $248.90  
  7 purchase totals = $823.44       $880.6878   $880.69   $880.70   $880.70