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 $70.90   7.153%   $75.9715   $75.97   $75.95   $76.00  
  Purchase #2 $155.39   10.325%   $171.434   $171.43   $171.45   $171.40  
  Purchase #3 $126.53   4.378%   $132.0695   $132.07   $132.05   $132.10  
  Purchase #4 $227.58   5.399%   $239.867   $239.87   $239.85   $239.90  
  Purchase #5 $66.74   7.527%   $71.7635   $71.76   $71.75   $71.80  
  Purchase #6 $195.50   9.703%   $214.4694   $214.47   $214.45   $214.50  
  Purchase #7 $84.71   9.324%   $92.6084   $92.61   $92.60   $92.60  
  7 purchase totals = $927.35       $998.1833   $998.18   $998.10   $998.30