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 $207.42   12.371%   $233.0799   $233.08   $233.10   $233.10  
  Purchase #2 $119.30   3.354%   $123.3013   $123.30   $123.30   $123.30  
  Purchase #3 $185.47   7.149%   $198.7293   $198.73   $198.75   $198.70  
  Purchase #4 $126.32   3.652%   $130.9332   $130.93   $130.95   $130.90  
  Purchase #5 $23.28   12.312%   $26.1462   $26.15   $26.15   $26.10  
  Purchase #6 $213.58   9.233%   $233.2998   $233.30   $233.30   $233.30  
  Purchase #7 $146.60   6.662%   $156.3665   $156.37   $156.35   $156.40  
  7 purchase totals = $1,021.97       $1,101.8562   $1,101.86   $1,101.90   $1,101.80