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 $32.87   3.857%   $34.1378   $34.14   $34.15   $34.10  
  Purchase #2 $39.73   12.169%   $44.5647   $44.56   $44.55   $44.60  
  Purchase #3 $46.33   8.748%   $50.3829   $50.38   $50.40   $50.40  
  Purchase #4 $85.97   11.533%   $95.8849   $95.88   $95.90   $95.90  
  Purchase #5 $229.29   13.115%   $259.3614   $259.36   $259.35   $259.40  
  Purchase #6 $138.73   10.871%   $153.8113   $153.81   $153.80   $153.80  
  Purchase #7 $239.34   8.805%   $260.4139   $260.41   $260.40   $260.40  
  7 purchase totals = $812.26       $898.5569   $898.54   $898.55   $898.60