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 $27.28   10.831%   $30.2347   $30.23   $30.25   $30.20  
  Purchase #2 $213.62   6.587%   $227.6911   $227.69   $227.70   $227.70  
  Purchase #3 $195.30   8.852%   $212.588   $212.59   $212.60   $212.60  
  Purchase #4 $224.37   13.589%   $254.8596   $254.86   $254.85   $254.90  
  Purchase #5 $112.56   12.758%   $126.9204   $126.92   $126.90   $126.90  
  Purchase #6 $68.86   6.382%   $73.2546   $73.25   $73.25   $73.30  
  Purchase #7 $23.44   3.340%   $24.2229   $24.22   $24.20   $24.20  
  7 purchase totals = $865.43       $949.7713   $949.76   $949.75   $949.80