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 $239.99   9.109%   $261.8507   $261.85   $261.85   $261.90  
  Purchase #2 $122.99   4.277%   $128.2503   $128.25   $128.25   $128.30  
  Purchase #3 $221.28   9.542%   $242.3945   $242.39   $242.40   $242.40  
  Purchase #4 $141.87   5.623%   $149.8474   $149.85   $149.85   $149.80  
  Purchase #5 $42.62   3.331%   $44.0397   $44.04   $44.05   $44.00  
  Purchase #6 $75.79   8.566%   $82.2822   $82.28   $82.30   $82.30  
  Purchase #7 $215.85   11.197%   $240.0187   $240.02   $240.00   $240.00  
  7 purchase totals = $1,060.39       $1,148.6835   $1,148.68   $1,148.70   $1,148.70