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 $151.58   8.354%   $164.243   $164.24   $164.25   $164.20  
  Purchase #2 $160.98   7.781%   $173.5059   $173.51   $173.50   $173.50  
  Purchase #3 $170.74   13.412%   $193.6396   $193.64   $193.65   $193.60  
  Purchase #4 $242.43   5.595%   $255.994   $255.99   $256.00   $256.00  
  Purchase #5 $125.66   8.701%   $136.5937   $136.59   $136.60   $136.60  
  Purchase #6 $192.83   13.364%   $218.5998   $218.60   $218.60   $218.60  
  Purchase #7 $90.59   12.274%   $101.709   $101.71   $101.70   $101.70  
  7 purchase totals = $1,134.81       $1,244.2850   $1,244.28   $1,244.30   $1,244.20