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 $54.82   13.220%   $62.0672   $62.07   $62.05   $62.10  
  Purchase #2 $222.99   11.428%   $248.4733   $248.47   $248.45   $248.50  
  Purchase #3 $133.38   7.307%   $143.1261   $143.13   $143.15   $143.10  
  Purchase #4 $206.33   9.492%   $225.9148   $225.91   $225.90   $225.90  
  Purchase #5 $43.64   10.231%   $48.1048   $48.10   $48.10   $48.10  
  Purchase #6 $69.26   8.843%   $75.3847   $75.38   $75.40   $75.40  
  Purchase #7 $38.83   8.667%   $42.1954   $42.20   $42.20   $42.20  
  7 purchase totals = $769.25       $845.2663   $845.26   $845.25   $845.30