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 $84.82   11.336%   $94.4352   $94.44   $94.45   $94.40  
  Purchase #2 $246.91   5.697%   $260.9765   $260.98   $261.00   $261.00  
  Purchase #3 $11.33   3.716%   $11.751   $11.75   $11.75   $11.80  
  Purchase #4 $40.82   4.562%   $42.6822   $42.68   $42.70   $42.70  
  Purchase #5 $196.55   11.189%   $218.542   $218.54   $218.55   $218.50  
  Purchase #6 $105.34   4.485%   $110.0645   $110.06   $110.05   $110.10  
  Purchase #7 $185.69   6.566%   $197.8824   $197.88   $197.90   $197.90  
  7 purchase totals = $871.46       $936.3338   $936.33   $936.40   $936.40