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 $122.37   11.551%   $136.505   $136.51   $136.50   $136.50  
  Purchase #2 $44.71   5.675%   $47.2473   $47.25   $47.25   $47.20  
  Purchase #3 $44.39   9.611%   $48.6563   $48.66   $48.65   $48.70  
  Purchase #4 $230.38   3.237%   $237.8374   $237.84   $237.85   $237.80  
  Purchase #5 $215.93   9.378%   $236.1799   $236.18   $236.20   $236.20  
  Purchase #6 $247.73   5.779%   $262.0463   $262.05   $262.05   $262.00  
  Purchase #7 $90.90   7.732%   $97.9284   $97.93   $97.95   $97.90  
  7 purchase totals = $996.41       $1,066.4006   $1,066.42   $1,066.45   $1,066.30