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 $48.97   11.866%   $54.7808   $54.78   $54.80   $54.80  
  Purchase #2 $5.90   10.193%   $6.5014   $6.50   $6.50   $6.50  
  Purchase #3 $239.31   9.645%   $262.3914   $262.39   $262.40   $262.40  
  Purchase #4 $168.77   9.807%   $185.3213   $185.32   $185.30   $185.30  
  Purchase #5 $140.93   7.125%   $150.9713   $150.97   $150.95   $151.00  
  Purchase #6 $84.26   7.679%   $90.7303   $90.73   $90.75   $90.70  
  Purchase #7 $191.95   7.184%   $205.7397   $205.74   $205.75   $205.70  
  7 purchase totals = $880.09       $956.4362   $956.43   $956.45   $956.40