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 $44.77   10.770%   $49.5917   $49.59   $49.60   $49.60  
  Purchase #2 $36.55   11.862%   $40.8856   $40.89   $40.90   $40.90  
  Purchase #3 $232.54   12.575%   $261.7819   $261.78   $261.80   $261.80  
  Purchase #4 $240.44   6.790%   $256.7659   $256.77   $256.75   $256.80  
  Purchase #5 $23.55   6.120%   $24.9913   $24.99   $25.00   $25.00  
  Purchase #6 $102.29   11.730%   $114.2886   $114.29   $114.30   $114.30  
  Purchase #7 $32.87   8.412%   $35.635   $35.64   $35.65   $35.60  
  7 purchase totals = $713.01       $783.9400   $783.95   $784.00   $784.00