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 $107.29   6.478%   $114.2402   $114.24   $114.25   $114.20  
  Purchase #2 $216.63   12.629%   $243.9882   $243.99   $244.00   $244.00  
  Purchase #3 $104.72   11.692%   $116.9639   $116.96   $116.95   $117.00  
  Purchase #4 $234.38   5.787%   $247.9436   $247.94   $247.95   $247.90  
  Purchase #5 $84.79   11.487%   $94.5298   $94.53   $94.55   $94.50  
  Purchase #6 $114.62   6.338%   $121.8846   $121.88   $121.90   $121.90  
  Purchase #7 $21.29   4.179%   $22.1797   $22.18   $22.20   $22.20  
  7 purchase totals = $883.72       $961.7300   $961.72   $961.80   $961.70