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 $233.37   11.277%   $259.6871   $259.69   $259.70   $259.70  
  Purchase #2 $63.53   4.773%   $66.5623   $66.56   $66.55   $66.60  
  Purchase #3 $69.69   7.199%   $74.707   $74.71   $74.70   $74.70  
  Purchase #4 $208.34   7.539%   $224.0468   $224.05   $224.05   $224.00  
  Purchase #5 $229.36   3.338%   $237.016   $237.02   $237.00   $237.00  
  Purchase #6 $8.66   13.378%   $9.8185   $9.82   $9.80   $9.80  
  Purchase #7 $159.41   7.809%   $171.8583   $171.86   $171.85   $171.90  
  7 purchase totals = $972.36       $1,043.6960   $1,043.71   $1,043.65   $1,043.70