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 $43.57   11.330%   $48.5065   $48.51   $48.50   $48.50  
  Purchase #2 $159.71   9.354%   $174.6493   $174.65   $174.65   $174.60  
  Purchase #3 $239.25   6.593%   $255.0238   $255.02   $255.00   $255.00  
  Purchase #4 $91.49   11.833%   $102.316   $102.32   $102.30   $102.30  
  Purchase #5 $101.30   11.807%   $113.2605   $113.26   $113.25   $113.30  
  Purchase #6 $249.72   11.493%   $278.4203   $278.42   $278.40   $278.40  
  Purchase #7 $189.93   4.660%   $198.7807   $198.78   $198.80   $198.80  
  7 purchase totals = $1,074.97       $1,170.9571   $1,170.96   $1,170.90   $1,170.90