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 $101.56   11.252%   $112.9875   $112.99   $113.00   $113.00  
  Purchase #2 $46.63   11.353%   $51.9239   $51.92   $51.90   $51.90  
  Purchase #3 $118.29   12.114%   $132.6197   $132.62   $132.60   $132.60  
  Purchase #4 $169.38   9.682%   $185.7794   $185.78   $185.80   $185.80  
  Purchase #5 $45.94   4.404%   $47.9632   $47.96   $47.95   $48.00  
  Purchase #6 $203.53   9.563%   $222.9936   $222.99   $223.00   $223.00  
  Purchase #7 $107.94   10.248%   $119.0017   $119.00   $119.00   $119.00  
  7 purchase totals = $793.27       $873.2690   $873.26   $873.25   $873.30