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 $59.77   11.476%   $66.6292   $66.63   $66.65   $66.60  
  Purchase #2 $172.71   13.255%   $195.6027   $195.60   $195.60   $195.60  
  Purchase #3 $112.99   5.644%   $119.3672   $119.37   $119.35   $119.40  
  Purchase #4 $24.74   12.834%   $27.9151   $27.92   $27.90   $27.90  
  Purchase #5 $215.41   11.319%   $239.7923   $239.79   $239.80   $239.80  
  Purchase #6 $143.94   11.266%   $160.1563   $160.16   $160.15   $160.20  
  Purchase #7 $33.32   12.206%   $37.387   $37.39   $37.40   $37.40  
  7 purchase totals = $762.88       $846.8498   $846.86   $846.85   $846.90