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 $214.86   12.684%   $242.1128   $242.11   $242.10   $242.10  
  Purchase #2 $194.94   13.859%   $221.9567   $221.96   $221.95   $222.00  
  Purchase #3 $34.75   4.266%   $36.2324   $36.23   $36.25   $36.20  
  Purchase #4 $230.68   7.681%   $248.3985   $248.40   $248.40   $248.40  
  Purchase #5 $13.29   10.500%   $14.6855   $14.69   $14.70   $14.70  
  Purchase #6 $97.28   5.293%   $102.429   $102.43   $102.45   $102.40  
  Purchase #7 $87.38   4.856%   $91.6232   $91.62   $91.60   $91.60  
  7 purchase totals = $873.18       $957.4381   $957.44   $957.45   $957.40