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 $219.82   10.168%   $242.1713   $242.17   $242.15   $242.20  
  Purchase #2 $205.97   4.751%   $215.7556   $215.76   $215.75   $215.80  
  Purchase #3 $148.34   4.311%   $154.7349   $154.73   $154.75   $154.70  
  Purchase #4 $175.77   10.163%   $193.6335   $193.63   $193.65   $193.60  
  Purchase #5 $180.89   3.632%   $187.4599   $187.46   $187.45   $187.50  
  Purchase #6 $72.32   6.427%   $76.968   $76.97   $76.95   $77.00  
  Purchase #7 $196.66   10.421%   $217.1539   $217.15   $217.15   $217.20  
  7 purchase totals = $1,199.77       $1,287.8771   $1,287.87   $1,287.85   $1,288.00