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 $78.70   4.452%   $82.2037   $82.20   $82.20   $82.20  
  Purchase #2 $232.94   3.176%   $240.3382   $240.34   $240.35   $240.30  
  Purchase #3 $156.26   3.608%   $161.8979   $161.90   $161.90   $161.90  
  Purchase #4 $226.31   8.441%   $245.4128   $245.41   $245.40   $245.40  
  Purchase #5 $206.77   9.257%   $225.9107   $225.91   $225.90   $225.90  
  Purchase #6 $205.73   13.608%   $233.7257   $233.73   $233.75   $233.70  
  Purchase #7 $248.46   11.741%   $277.6317   $277.63   $277.65   $277.60  
  7 purchase totals = $1,355.17       $1,467.1207   $1,467.12   $1,467.15   $1,467.00