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 $249.27   11.109%   $276.9614   $276.96   $276.95   $277.00  
  Purchase #2 $26.56   10.779%   $29.4229   $29.42   $29.40   $29.40  
  Purchase #3 $215.77   12.546%   $242.8405   $242.84   $242.85   $242.80  
  Purchase #4 $225.92   4.789%   $236.7393   $236.74   $236.75   $236.70  
  Purchase #5 $115.94   8.520%   $125.8181   $125.82   $125.80   $125.80  
  Purchase #6 $113.91   13.615%   $129.4188   $129.42   $129.40   $129.40  
  Purchase #7 $173.96   4.683%   $182.1065   $182.11   $182.10   $182.10  
  7 purchase totals = $1,121.33       $1,223.3075   $1,223.31   $1,223.25   $1,223.20