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 $246.25   11.355%   $274.2117   $274.21   $274.20   $274.20  
  Purchase #2 $235.49   13.169%   $266.5017   $266.50   $266.50   $266.50  
  Purchase #3 $224.58   9.125%   $245.0729   $245.07   $245.05   $245.10  
  Purchase #4 $64.56   7.769%   $69.5757   $69.58   $69.60   $69.60  
  Purchase #5 $157.63   11.729%   $176.1184   $176.12   $176.10   $176.10  
  Purchase #6 $222.31   3.626%   $230.371   $230.37   $230.35   $230.40  
  Purchase #7 $145.77   11.365%   $162.3368   $162.34   $162.35   $162.30  
  7 purchase totals = $1,296.59       $1,424.1882   $1,424.19   $1,424.15   $1,424.20