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 $53.99   11.719%   $60.3171   $60.32   $60.30   $60.30  
  Purchase #2 $59.62   3.795%   $61.8826   $61.88   $61.90   $61.90  
  Purchase #3 $229.29   4.318%   $239.1907   $239.19   $239.20   $239.20  
  Purchase #4 $25.39   10.430%   $28.0382   $28.04   $28.05   $28.00  
  Purchase #5 $86.61   6.682%   $92.3973   $92.40   $92.40   $92.40  
  Purchase #6 $49.85   8.534%   $54.1042   $54.10   $54.10   $54.10  
  Purchase #7 $228.73   3.657%   $237.0947   $237.09   $237.10   $237.10  
  7 purchase totals = $733.48       $773.0248   $773.02   $773.05   $773.00