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 $66.39   10.266%   $73.2056   $73.21   $73.20   $73.20  
  Purchase #2 $32.84   12.848%   $37.0593   $37.06   $37.05   $37.10  
  Purchase #3 $158.32   6.271%   $168.2482   $168.25   $168.25   $168.20  
  Purchase #4 $10.87   13.647%   $12.3534   $12.35   $12.35   $12.40  
  Purchase #5 $247.29   5.664%   $261.2965   $261.30   $261.30   $261.30  
  Purchase #6 $39.69   7.267%   $42.5743   $42.57   $42.55   $42.60  
  Purchase #7 $114.66   4.658%   $120.0009   $120.00   $120.00   $120.00  
  7 purchase totals = $670.06       $714.7382   $714.74   $714.70   $714.80