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 $62.67   13.847%   $71.3479   $71.35   $71.35   $71.30  
  Purchase #2 $196.42   6.661%   $209.5035   $209.50   $209.50   $209.50  
  Purchase #3 $209.55   9.389%   $229.2246   $229.22   $229.20   $229.20  
  Purchase #4 $124.40   4.244%   $129.6795   $129.68   $129.70   $129.70  
  Purchase #5 $69.83   9.319%   $76.3375   $76.34   $76.35   $76.30  
  Purchase #6 $172.60   10.228%   $190.2535   $190.25   $190.25   $190.30  
  Purchase #7 $18.55   3.686%   $19.2338   $19.23   $19.25   $19.20  
  7 purchase totals = $854.02       $925.5803   $925.57   $925.60   $925.50