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 $223.93   11.418%   $249.4983   $249.50   $249.50   $249.50  
  Purchase #2 $97.93   10.569%   $108.2802   $108.28   $108.30   $108.30  
  Purchase #3 $59.72   12.244%   $67.0321   $67.03   $67.05   $67.00  
  Purchase #4 $53.66   6.533%   $57.1656   $57.17   $57.15   $57.20  
  Purchase #5 $194.35   5.309%   $204.668   $204.67   $204.65   $204.70  
  Purchase #6 $57.88   11.783%   $64.7   $64.70   $64.70   $64.70  
  Purchase #7 $174.53   4.787%   $182.8848   $182.88   $182.90   $182.90  
  7 purchase totals = $862.00       $934.2290   $934.23   $934.25   $934.30