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 $112.30   12.243%   $126.0489   $126.05   $126.05   $126.00  
  Purchase #2 $212.43   11.711%   $237.3077   $237.31   $237.30   $237.30  
  Purchase #3 $90.63   9.616%   $99.345   $99.35   $99.35   $99.30  
  Purchase #4 $250.37   9.800%   $274.9063   $274.91   $274.90   $274.90  
  Purchase #5 $240.77   8.821%   $262.0083   $262.01   $262.00   $262.00  
  Purchase #6 $208.71   9.573%   $228.6898   $228.69   $228.70   $228.70  
  Purchase #7 $189.76   5.140%   $199.5137   $199.51   $199.50   $199.50  
  7 purchase totals = $1,304.97       $1,427.8197   $1,427.83   $1,427.80   $1,427.70