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 $169.93   9.394%   $185.8932   $185.89   $185.90   $185.90  
  Purchase #2 $14.80   9.191%   $16.1603   $16.16   $16.15   $16.20  
  Purchase #3 $250.87   6.443%   $267.0336   $267.03   $267.05   $267.00  
  Purchase #4 $123.88   7.144%   $132.73   $132.73   $132.75   $132.70  
  Purchase #5 $52.62   6.271%   $55.9198   $55.92   $55.90   $55.90  
  Purchase #6 $32.95   4.465%   $34.4212   $34.42   $34.40   $34.40  
  Purchase #7 $56.50   6.246%   $60.029   $60.03   $60.05   $60.00  
  7 purchase totals = $701.55       $752.1871   $752.18   $752.20   $752.10