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 $248.70   7.825%   $268.1608   $268.16   $268.15   $268.20  
  Purchase #2 $129.26   6.690%   $137.9075   $137.91   $137.90   $137.90  
  Purchase #3 $112.65   3.649%   $116.7606   $116.76   $116.75   $116.80  
  Purchase #4 $236.55   8.770%   $257.2954   $257.30   $257.30   $257.30  
  Purchase #5 $13.99   12.576%   $15.7494   $15.75   $15.75   $15.70  
  Purchase #6 $204.80   8.178%   $221.5485   $221.55   $221.55   $221.50  
  Purchase #7 $48.77   10.508%   $53.8948   $53.89   $53.90   $53.90  
  7 purchase totals = $994.72       $1,071.3170   $1,071.32   $1,071.30   $1,071.30