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 $242.93   7.686%   $261.6016   $261.60   $261.60   $261.60  
  Purchase #2 $129.67   10.825%   $143.7068   $143.71   $143.70   $143.70  
  Purchase #3 $48.55   3.685%   $50.3391   $50.34   $50.35   $50.30  
  Purchase #4 $84.89   8.833%   $92.3883   $92.39   $92.40   $92.40  
  Purchase #5 $187.63   3.563%   $194.3153   $194.32   $194.30   $194.30  
  Purchase #6 $14.81   11.788%   $16.5558   $16.56   $16.55   $16.60  
  Purchase #7 $95.47   6.233%   $101.4206   $101.42   $101.40   $101.40  
  7 purchase totals = $803.95       $860.3275   $860.34   $860.30   $860.30