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 $175.41   9.763%   $192.5353   $192.54   $192.55   $192.50  
  Purchase #2 $210.93   12.316%   $236.9081   $236.91   $236.90   $236.90  
  Purchase #3 $57.29   5.384%   $60.3745   $60.37   $60.35   $60.40  
  Purchase #4 $34.29   12.682%   $38.6387   $38.64   $38.65   $38.60  
  Purchase #5 $171.68   4.542%   $179.4777   $179.48   $179.50   $179.50  
  Purchase #6 $243.96   7.191%   $261.5032   $261.50   $261.50   $261.50  
  Purchase #7 $73.76   10.495%   $81.5011   $81.50   $81.50   $81.50  
  7 purchase totals = $967.32       $1,050.9386   $1,050.94   $1,050.95   $1,050.90