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 $84.83   13.562%   $96.3346   $96.33   $96.35   $96.30  
  Purchase #2 $125.99   10.477%   $139.19   $139.19   $139.20   $139.20  
  Purchase #3 $173.79   12.292%   $195.1523   $195.15   $195.15   $195.20  
  Purchase #4 $26.44   6.612%   $28.1882   $28.19   $28.20   $28.20  
  Purchase #5 $151.96   4.387%   $158.6265   $158.63   $158.65   $158.60  
  Purchase #6 $65.82   4.110%   $68.5252   $68.53   $68.55   $68.50  
  Purchase #7 $208.32   3.261%   $215.1133   $215.11   $215.10   $215.10  
  7 purchase totals = $837.15       $901.1301   $901.13   $901.20   $901.10