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 $234.26   13.842%   $266.6863   $266.69   $266.70   $266.70  
  Purchase #2 $193.68   6.830%   $206.9083   $206.91   $206.90   $206.90  
  Purchase #3 $51.65   5.623%   $54.5543   $54.55   $54.55   $54.60  
  Purchase #4 $144.95   7.112%   $155.2588   $155.26   $155.25   $155.30  
  Purchase #5 $169.85   7.763%   $183.0355   $183.04   $183.05   $183.00  
  Purchase #6 $125.38   12.429%   $140.9635   $140.96   $140.95   $141.00  
  Purchase #7 $248.38   6.774%   $265.2053   $265.21   $265.20   $265.20  
  7 purchase totals = $1,168.15       $1,272.6120   $1,272.62   $1,272.60   $1,272.70