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 $48.43   4.659%   $50.6864   $50.69   $50.70   $50.70  
  Purchase #2 $225.50   9.130%   $246.0882   $246.09   $246.10   $246.10  
  Purchase #3 $246.46   5.649%   $260.3825   $260.38   $260.40   $260.40  
  Purchase #4 $246.98   7.863%   $266.4   $266.40   $266.40   $266.40  
  Purchase #5 $162.79   11.811%   $182.0171   $182.02   $182.00   $182.00  
  Purchase #6 $161.49   10.509%   $178.461   $178.46   $178.45   $178.50  
  Purchase #7 $92.64   5.821%   $98.0326   $98.03   $98.05   $98.00  
  7 purchase totals = $1,184.29       $1,282.0678   $1,282.07   $1,282.10   $1,282.10