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 $245.69   6.352%   $261.2962   $261.30   $261.30   $261.30  
  Purchase #2 $250.97   9.707%   $275.3317   $275.33   $275.35   $275.30  
  Purchase #3 $224.89   6.282%   $239.0176   $239.02   $239.00   $239.00  
  Purchase #4 $57.83   4.828%   $60.622   $60.62   $60.60   $60.60  
  Purchase #5 $14.59   4.728%   $15.2798   $15.28   $15.30   $15.30  
  Purchase #6 $244.59   9.608%   $268.0902   $268.09   $268.10   $268.10  
  Purchase #7 $69.92   5.290%   $73.6188   $73.62   $73.60   $73.60  
  7 purchase totals = $1,108.48       $1,193.2563   $1,193.26   $1,193.25   $1,193.20