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 $239.26   6.158%   $253.9936   $253.99   $254.00   $254.00  
  Purchase #2 $91.55   4.665%   $95.8208   $95.82   $95.80   $95.80  
  Purchase #3 $30.27   3.714%   $31.3942   $31.39   $31.40   $31.40  
  Purchase #4 $151.87   7.714%   $163.5853   $163.59   $163.60   $163.60  
  Purchase #5 $13.48   10.643%   $14.9147   $14.91   $14.90   $14.90  
  Purchase #6 $208.76   11.806%   $233.4062   $233.41   $233.40   $233.40  
  Purchase #7 $216.98   6.417%   $230.9036   $230.90   $230.90   $230.90  
  7 purchase totals = $952.17       $1,024.0184   $1,024.01   $1,024.00   $1,024.00