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 $206.50   13.710%   $234.8112   $234.81   $234.80   $234.80  
  Purchase #2 $244.62   13.652%   $278.0155   $278.02   $278.00   $278.00  
  Purchase #3 $31.82   9.248%   $34.7627   $34.76   $34.75   $34.80  
  Purchase #4 $126.91   13.423%   $143.9451   $143.95   $143.95   $143.90  
  Purchase #5 $116.85   7.775%   $125.9351   $125.94   $125.95   $125.90  
  Purchase #6 $207.63   12.149%   $232.855   $232.86   $232.85   $232.90  
  Purchase #7 $198.59   12.750%   $223.9102   $223.91   $223.90   $223.90  
  7 purchase totals = $1,132.92       $1,274.2348   $1,274.25   $1,274.20   $1,274.20