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 $45.41   11.504%   $50.634   $50.63   $50.65   $50.60  
  Purchase #2 $208.34   3.393%   $215.409   $215.41   $215.40   $215.40  
  Purchase #3 $113.78   6.251%   $120.8924   $120.89   $120.90   $120.90  
  Purchase #4 $188.28   10.317%   $207.7048   $207.70   $207.70   $207.70  
  Purchase #5 $43.27   6.388%   $46.0341   $46.03   $46.05   $46.00  
  Purchase #6 $21.77   9.870%   $23.9187   $23.92   $23.90   $23.90  
  Purchase #7 $131.48   6.609%   $140.1695   $140.17   $140.15   $140.20  
  7 purchase totals = $752.33       $804.7625   $804.75   $804.75   $804.70