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 $64.94   3.641%   $67.3045   $67.30   $67.30   $67.30  
  Purchase #2 $86.73   7.663%   $93.3761   $93.38   $93.40   $93.40  
  Purchase #3 $224.40   9.400%   $245.4936   $245.49   $245.50   $245.50  
  Purchase #4 $87.33   11.557%   $97.4227   $97.42   $97.40   $97.40  
  Purchase #5 $154.36   3.261%   $159.3937   $159.39   $159.40   $159.40  
  Purchase #6 $82.49   10.783%   $91.3849   $91.38   $91.40   $91.40  
  Purchase #7 $199.37   7.535%   $214.3925   $214.39   $214.40   $214.40  
  7 purchase totals = $899.62       $968.7680   $968.75   $968.80   $968.80