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 $117.42   6.467%   $125.0136   $125.01   $125.00   $125.00  
  Purchase #2 $84.96   12.366%   $95.4662   $95.47   $95.45   $95.50  
  Purchase #3 $226.72   10.809%   $251.2262   $251.23   $251.25   $251.20  
  Purchase #4 $166.30   11.694%   $185.7471   $185.75   $185.75   $185.70  
  Purchase #5 $65.57   3.298%   $67.7325   $67.73   $67.75   $67.70  
  Purchase #6 $250.99   4.158%   $261.4262   $261.43   $261.45   $261.40  
  Purchase #7 $153.50   7.474%   $164.9726   $164.97   $164.95   $165.00  
  7 purchase totals = $1,065.46       $1,151.5844   $1,151.59   $1,151.60   $1,151.50