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 $250.39   4.538%   $261.7527   $261.75   $261.75   $261.80  
  Purchase #2 $64.39   3.491%   $66.6379   $66.64   $66.65   $66.60  
  Purchase #3 $158.84   5.523%   $167.6127   $167.61   $167.60   $167.60  
  Purchase #4 $14.30   5.503%   $15.0869   $15.09   $15.10   $15.10  
  Purchase #5 $220.43   7.183%   $236.2635   $236.26   $236.25   $236.30  
  Purchase #6 $80.79   10.542%   $89.3069   $89.31   $89.30   $89.30  
  Purchase #7 $61.70   8.423%   $66.897   $66.90   $66.90   $66.90  
  7 purchase totals = $850.84       $903.5576   $903.56   $903.55   $903.60