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 $232.54   9.174%   $253.8732   $253.87   $253.85   $253.90  
  Purchase #2 $179.97   3.697%   $186.6235   $186.62   $186.60   $186.60  
  Purchase #3 $227.79   8.435%   $247.0041   $247.00   $247.00   $247.00  
  Purchase #4 $94.44   6.298%   $100.3878   $100.39   $100.40   $100.40  
  Purchase #5 $82.98   3.171%   $85.6113   $85.61   $85.60   $85.60  
  Purchase #6 $67.39   9.522%   $73.8069   $73.81   $73.80   $73.80  
  Purchase #7 $233.48   11.803%   $261.0376   $261.04   $261.05   $261.00  
  7 purchase totals = $1,118.59       $1,208.3444   $1,208.34   $1,208.30   $1,208.30