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 $125.27   8.731%   $136.2073   $136.21   $136.20   $136.20  
  Purchase #2 $209.83   8.734%   $228.1566   $228.16   $228.15   $228.20  
  Purchase #3 $135.99   11.686%   $151.8818   $151.88   $151.90   $151.90  
  Purchase #4 $228.69   13.556%   $259.6912   $259.69   $259.70   $259.70  
  Purchase #5 $112.36   5.647%   $118.705   $118.71   $118.70   $118.70  
  Purchase #6 $127.84   5.128%   $134.3956   $134.40   $134.40   $134.40  
  Purchase #7 $229.25   6.532%   $244.2246   $244.22   $244.20   $244.20  
  7 purchase totals = $1,169.23       $1,273.2621   $1,273.27   $1,273.25   $1,273.30