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 $73.82   4.606%   $77.2201   $77.22   $77.20   $77.20  
  Purchase #2 $215.77   8.184%   $233.4286   $233.43   $233.45   $233.40  
  Purchase #3 $168.37   3.816%   $174.795   $174.80   $174.80   $174.80  
  Purchase #4 $45.91   10.462%   $50.7131   $50.71   $50.70   $50.70  
  Purchase #5 $230.47   13.355%   $261.2493   $261.25   $261.25   $261.20  
  Purchase #6 $239.29   11.317%   $266.3704   $266.37   $266.35   $266.40  
  Purchase #7 $168.46   4.547%   $176.1199   $176.12   $176.10   $176.10  
  7 purchase totals = $1,142.09       $1,239.8964   $1,239.90   $1,239.85   $1,239.80