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 $250.46   10.531%   $276.8359   $276.84   $276.85   $276.80  
  Purchase #2 $241.86   5.247%   $254.5504   $254.55   $254.55   $254.60  
  Purchase #3 $12.93   13.397%   $14.6622   $14.66   $14.65   $14.70  
  Purchase #4 $215.94   13.135%   $244.3037   $244.30   $244.30   $244.30  
  Purchase #5 $237.87   3.699%   $246.6688   $246.67   $246.65   $246.70  
  Purchase #6 $168.26   12.157%   $188.7154   $188.72   $188.70   $188.70  
  Purchase #7 $218.49   10.774%   $242.0301   $242.03   $242.05   $242.00  
  7 purchase totals = $1,345.81       $1,467.7665   $1,467.77   $1,467.75   $1,467.80