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 $96.42   5.461%   $101.6855   $101.69   $101.70   $101.70  
  Purchase #2 $118.78   4.113%   $123.6654   $123.67   $123.65   $123.70  
  Purchase #3 $48.79   4.349%   $50.9119   $50.91   $50.90   $50.90  
  Purchase #4 $42.51   5.537%   $44.8638   $44.86   $44.85   $44.90  
  Purchase #5 $27.89   8.125%   $30.1561   $30.16   $30.15   $30.20  
  Purchase #6 $118.56   12.485%   $133.3622   $133.36   $133.35   $133.40  
  Purchase #7 $160.99   9.105%   $175.6481   $175.65   $175.65   $175.60  
  7 purchase totals = $613.94       $660.2930   $660.30   $660.25   $660.40