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 $244.94   6.547%   $260.9762   $260.98   $261.00   $261.00  
  Purchase #2 $209.30   3.497%   $216.6192   $216.62   $216.60   $216.60  
  Purchase #3 $78.44   10.343%   $86.553   $86.55   $86.55   $86.60  
  Purchase #4 $200.41   10.540%   $221.5332   $221.53   $221.55   $221.50  
  Purchase #5 $135.32   6.739%   $144.4392   $144.44   $144.45   $144.40  
  Purchase #6 $126.93   5.213%   $133.5469   $133.55   $133.55   $133.50  
  Purchase #7 $188.45   12.658%   $212.304   $212.30   $212.30   $212.30  
  7 purchase totals = $1,183.79       $1,275.9717   $1,275.97   $1,276.00   $1,275.90