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 $91.54   6.549%   $97.535   $97.54   $97.55   $97.50  
  Purchase #2 $157.43   8.210%   $170.355   $170.36   $170.35   $170.40  
  Purchase #3 $69.49   6.506%   $74.011   $74.01   $74.00   $74.00  
  Purchase #4 $143.51   13.392%   $162.7289   $162.73   $162.75   $162.70  
  Purchase #5 $54.26   5.602%   $57.2996   $57.30   $57.30   $57.30  
  Purchase #6 $191.88   13.565%   $217.9085   $217.91   $217.90   $217.90  
  Purchase #7 $115.33   13.378%   $130.7588   $130.76   $130.75   $130.80  
  7 purchase totals = $823.44       $910.5968   $910.61   $910.60   $910.60