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 $50.48   5.741%   $53.3781   $53.38   $53.40   $53.40  
  Purchase #2 $232.92   6.350%   $247.7104   $247.71   $247.70   $247.70  
  Purchase #3 $124.60   7.287%   $133.6796   $133.68   $133.70   $133.70  
  Purchase #4 $26.42   4.395%   $27.5812   $27.58   $27.60   $27.60  
  Purchase #5 $57.90   10.846%   $64.1798   $64.18   $64.20   $64.20  
  Purchase #6 $26.28   9.825%   $28.862   $28.86   $28.85   $28.90  
  Purchase #7 $170.73   4.431%   $178.295   $178.30   $178.30   $178.30  
  7 purchase totals = $689.33       $733.6861   $733.69   $733.75   $733.80