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 $84.71   11.124%   $94.1331   $94.13   $94.15   $94.10  
  Purchase #2 $222.49   4.143%   $231.7078   $231.71   $231.70   $231.70  
  Purchase #3 $135.68   3.175%   $139.9878   $139.99   $140.00   $140.00  
  Purchase #4 $50.30   11.452%   $56.0604   $56.06   $56.05   $56.10  
  Purchase #5 $242.29   12.798%   $273.2983   $273.30   $273.30   $273.30  
  Purchase #6 $239.86   11.288%   $266.9354   $266.94   $266.95   $266.90  
  Purchase #7 $182.39   6.638%   $194.497   $194.50   $194.50   $194.50  
  7 purchase totals = $1,157.72       $1,256.6198   $1,256.63   $1,256.65   $1,256.60