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 $237.55   10.211%   $261.8062   $261.81   $261.80   $261.80  
  Purchase #2 $174.44   13.104%   $197.2986   $197.30   $197.30   $197.30  
  Purchase #3 $107.70   7.800%   $116.1006   $116.10   $116.10   $116.10  
  Purchase #4 $220.97   12.841%   $249.3448   $249.34   $249.35   $249.30  
  Purchase #5 $75.96   9.660%   $83.2977   $83.30   $83.30   $83.30  
  Purchase #6 $228.69   13.716%   $260.0571   $260.06   $260.05   $260.10  
  Purchase #7 $23.70   10.354%   $26.1539   $26.15   $26.15   $26.20  
  7 purchase totals = $1,069.01       $1,194.0589   $1,194.06   $1,194.05   $1,194.10