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 $184.62   11.275%   $205.4359   $205.44   $205.45   $205.40  
  Purchase #2 $139.66   10.196%   $153.8997   $153.90   $153.90   $153.90  
  Purchase #3 $242.77   7.666%   $261.3807   $261.38   $261.40   $261.40  
  Purchase #4 $193.99   6.284%   $206.1803   $206.18   $206.20   $206.20  
  Purchase #5 $5.53   8.300%   $5.989   $5.99   $6.00   $6.00  
  Purchase #6 $108.49   10.155%   $119.5072   $119.51   $119.50   $119.50  
  Purchase #7 $12.85   7.819%   $13.8547   $13.85   $13.85   $13.90  
  7 purchase totals = $887.91       $966.2475   $966.25   $966.30   $966.30