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 $201.82   6.548%   $215.0352   $215.04   $215.05   $215.00  
  Purchase #2 $15.99   12.105%   $17.9256   $17.93   $17.95   $17.90  
  Purchase #3 $48.50   6.503%   $51.654   $51.65   $51.65   $51.70  
  Purchase #4 $80.48   3.505%   $83.3008   $83.30   $83.30   $83.30  
  Purchase #5 $231.28   4.788%   $242.3537   $242.35   $242.35   $242.40  
  Purchase #6 $49.44   7.383%   $53.0902   $53.09   $53.10   $53.10  
  Purchase #7 $93.36   11.682%   $104.2663   $104.27   $104.25   $104.30  
  7 purchase totals = $720.87       $767.6258   $767.63   $767.65   $767.70