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 $239.51   3.622%   $248.1851   $248.19   $248.20   $248.20  
  Purchase #2 $21.53   4.414%   $22.4803   $22.48   $22.50   $22.50  
  Purchase #3 $73.96   5.120%   $77.7468   $77.75   $77.75   $77.70  
  Purchase #4 $98.57   3.246%   $101.7696   $101.77   $101.75   $101.80  
  Purchase #5 $216.62   7.562%   $233.0008   $233.00   $233.00   $233.00  
  Purchase #6 $55.45   11.114%   $61.6127   $61.61   $61.60   $61.60  
  Purchase #7 $240.45   10.826%   $266.4811   $266.48   $266.50   $266.50  
  7 purchase totals = $946.09       $1,011.2764   $1,011.28   $1,011.30   $1,011.30