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 $82.62   13.183%   $93.5118   $93.51   $93.50   $93.50  
  Purchase #2 $167.96   12.207%   $188.4629   $188.46   $188.45   $188.50  
  Purchase #3 $199.77   5.563%   $210.8832   $210.88   $210.90   $210.90  
  Purchase #4 $175.53   12.509%   $197.487   $197.49   $197.50   $197.50  
  Purchase #5 $178.79   11.493%   $199.3383   $199.34   $199.35   $199.30  
  Purchase #6 $51.89   10.135%   $57.1491   $57.15   $57.15   $57.10  
  Purchase #7 $229.92   13.472%   $260.8948   $260.89   $260.90   $260.90  
  7 purchase totals = $1,086.48       $1,207.7271   $1,207.72   $1,207.75   $1,207.70