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 $227.35   7.457%   $244.3035   $244.30   $244.30   $244.30  
  Purchase #2 $236.86   6.198%   $251.5406   $251.54   $251.55   $251.50  
  Purchase #3 $11.51   8.105%   $12.4429   $12.44   $12.45   $12.40  
  Purchase #4 $140.25   12.452%   $157.7139   $157.71   $157.70   $157.70  
  Purchase #5 $68.77   5.178%   $72.3309   $72.33   $72.35   $72.30  
  Purchase #6 $168.65   8.143%   $182.3832   $182.38   $182.40   $182.40  
  Purchase #7 $165.49   4.791%   $173.4186   $173.42   $173.40   $173.40  
  7 purchase totals = $1,018.88       $1,094.1336   $1,094.12   $1,094.15   $1,094.00