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 $248.67   10.200%   $274.0343   $274.03   $274.05   $274.00  
  Purchase #2 $231.43   13.147%   $261.8561   $261.86   $261.85   $261.90  
  Purchase #3 $11.75   4.555%   $12.2852   $12.29   $12.30   $12.30  
  Purchase #4 $248.67   11.246%   $276.6354   $276.64   $276.65   $276.60  
  Purchase #5 $25.56   11.690%   $28.548   $28.55   $28.55   $28.50  
  Purchase #6 $245.36   10.518%   $271.167   $271.17   $271.15   $271.20  
  Purchase #7 $245.41   6.772%   $262.0292   $262.03   $262.05   $262.00  
  7 purchase totals = $1,256.85       $1,386.5552   $1,386.57   $1,386.60   $1,386.50