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 $101.49   12.678%   $114.3569   $114.36   $114.35   $114.40  
  Purchase #2 $50.89   9.312%   $55.6289   $55.63   $55.65   $55.60  
  Purchase #3 $51.43   6.475%   $54.7601   $54.76   $54.75   $54.80  
  Purchase #4 $240.96   7.216%   $258.3477   $258.35   $258.35   $258.30  
  Purchase #5 $235.60   8.357%   $255.2891   $255.29   $255.30   $255.30  
  Purchase #6 $12.80   8.871%   $13.9355   $13.94   $13.95   $13.90  
  Purchase #7 $190.44   6.430%   $202.6853   $202.69   $202.70   $202.70  
  7 purchase totals = $883.61       $955.0035   $955.02   $955.05   $955.00