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 $208.26   3.846%   $216.2697   $216.27   $216.25   $216.30  
  Purchase #2 $193.94   5.289%   $204.1975   $204.20   $204.20   $204.20  
  Purchase #3 $46.36   8.861%   $50.468   $50.47   $50.45   $50.50  
  Purchase #4 $89.48   4.269%   $93.2999   $93.30   $93.30   $93.30  
  Purchase #5 $127.34   13.418%   $144.4265   $144.43   $144.45   $144.40  
  Purchase #6 $163.71   3.164%   $168.8898   $168.89   $168.90   $168.90  
  Purchase #7 $107.82   8.707%   $117.2079   $117.21   $117.20   $117.20  
  7 purchase totals = $936.91       $994.7593   $994.77   $994.75   $994.80