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 $219.89   12.548%   $247.4818   $247.48   $247.50   $247.50  
  Purchase #2 $88.95   6.338%   $94.5877   $94.59   $94.60   $94.60  
  Purchase #3 $125.36   13.256%   $141.9777   $141.98   $142.00   $142.00  
  Purchase #4 $158.34   11.712%   $176.8848   $176.88   $176.90   $176.90  
  Purchase #5 $65.73   11.686%   $73.4112   $73.41   $73.40   $73.40  
  Purchase #6 $16.93   12.368%   $19.0239   $19.02   $19.00   $19.00  
  Purchase #7 $185.64   10.855%   $205.7912   $205.79   $205.80   $205.80  
  7 purchase totals = $860.84       $959.1583   $959.15   $959.20   $959.20