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 $57.51   11.785%   $64.2876   $64.29   $64.30   $64.30  
  Purchase #2 $226.99   7.600%   $244.2412   $244.24   $244.25   $244.20  
  Purchase #3 $145.34   5.653%   $153.5561   $153.56   $153.55   $153.60  
  Purchase #4 $213.71   11.161%   $237.5622   $237.56   $237.55   $237.60  
  Purchase #5 $9.69   12.501%   $10.9013   $10.90   $10.90   $10.90  
  Purchase #6 $17.70   11.874%   $19.8017   $19.80   $19.80   $19.80  
  Purchase #7 $58.80   5.139%   $61.8217   $61.82   $61.80   $61.80  
  7 purchase totals = $729.74       $792.1718   $792.17   $792.15   $792.20