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 $91.90   6.378%   $97.7614   $97.76   $97.75   $97.80  
  Purchase #2 $216.46   12.117%   $242.6885   $242.69   $242.70   $242.70  
  Purchase #3 $76.86   11.489%   $85.6904   $85.69   $85.70   $85.70  
  Purchase #4 $158.97   5.168%   $167.1856   $167.19   $167.20   $167.20  
  Purchase #5 $56.53   4.613%   $59.1377   $59.14   $59.15   $59.10  
  Purchase #6 $94.88   7.792%   $102.273   $102.27   $102.25   $102.30  
  Purchase #7 $229.37   3.167%   $236.6341   $236.63   $236.65   $236.60  
  7 purchase totals = $924.97       $991.3707   $991.37   $991.40   $991.40