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 $46.26   11.495%   $51.5776   $51.58   $51.60   $51.60  
  Purchase #2 $164.75   5.237%   $173.378   $173.38   $173.40   $173.40  
  Purchase #3 $226.98   4.186%   $236.4814   $236.48   $236.50   $236.50  
  Purchase #4 $179.94   6.289%   $191.2564   $191.26   $191.25   $191.30  
  Purchase #5 $90.64   5.622%   $95.7358   $95.74   $95.75   $95.70  
  Purchase #6 $49.60   8.741%   $53.9355   $53.94   $53.95   $53.90  
  Purchase #7 $11.26   9.574%   $12.338   $12.34   $12.35   $12.30  
  7 purchase totals = $769.43       $814.7027   $814.72   $814.80   $814.70