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 $97.61   6.299%   $103.7585   $103.76   $103.75   $103.80  
  Purchase #2 $44.83   12.665%   $50.5077   $50.51   $50.50   $50.50  
  Purchase #3 $52.64   13.608%   $59.8033   $59.80   $59.80   $59.80  
  Purchase #4 $86.41   11.554%   $96.3938   $96.39   $96.40   $96.40  
  Purchase #5 $158.78   3.236%   $163.9181   $163.92   $163.90   $163.90  
  Purchase #6 $125.70   12.749%   $141.7255   $141.73   $141.75   $141.70  
  Purchase #7 $8.68   9.862%   $9.536   $9.54   $9.55   $9.50  
  7 purchase totals = $574.65       $625.6429   $625.65   $625.65   $625.60