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 $186.92   10.271%   $206.1186   $206.12   $206.10   $206.10  
  Purchase #2 $238.25   12.290%   $267.5309   $267.53   $267.55   $267.50  
  Purchase #3 $94.36   3.492%   $97.6551   $97.66   $97.65   $97.70  
  Purchase #4 $165.93   6.311%   $176.4018   $176.40   $176.40   $176.40  
  Purchase #5 $225.41   13.660%   $256.201   $256.20   $256.20   $256.20  
  Purchase #6 $161.34   3.817%   $167.4983   $167.50   $167.50   $167.50  
  Purchase #7 $96.83   13.733%   $110.1277   $110.13   $110.15   $110.10  
  7 purchase totals = $1,169.04       $1,281.5334   $1,281.54   $1,281.55   $1,281.50