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 $94.38   9.361%   $103.2149   $103.21   $103.20   $103.20  
  Purchase #2 $198.83   13.225%   $225.1253   $225.13   $225.15   $225.10  
  Purchase #3 $51.44   12.257%   $57.745   $57.75   $57.75   $57.70  
  Purchase #4 $104.25   4.513%   $108.9548   $108.95   $108.95   $109.00  
  Purchase #5 $165.78   10.202%   $182.6929   $182.69   $182.70   $182.70  
  Purchase #6 $33.72   4.352%   $35.1875   $35.19   $35.20   $35.20  
  Purchase #7 $229.30   8.225%   $248.1599   $248.16   $248.15   $248.20  
  7 purchase totals = $877.70       $961.0803   $961.08   $961.10   $961.10