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 $67.98   13.636%   $77.2498   $77.25   $77.25   $77.20  
  Purchase #2 $127.85   5.508%   $134.892   $134.89   $134.90   $134.90  
  Purchase #3 $208.29   4.597%   $217.8651   $217.87   $217.85   $217.90  
  Purchase #4 $92.68   7.182%   $99.3363   $99.34   $99.35   $99.30  
  Purchase #5 $59.51   10.426%   $65.7145   $65.71   $65.70   $65.70  
  Purchase #6 $196.53   5.383%   $207.1092   $207.11   $207.10   $207.10  
  Purchase #7 $42.42   8.663%   $46.0948   $46.09   $46.10   $46.10  
  7 purchase totals = $795.26       $848.2617   $848.26   $848.25   $848.20