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 $200.85   3.534%   $207.948   $207.95   $207.95   $207.90  
  Purchase #2 $63.50   10.328%   $70.0583   $70.06   $70.05   $70.10  
  Purchase #3 $40.80   3.549%   $42.248   $42.25   $42.25   $42.20  
  Purchase #4 $210.86   7.493%   $226.6597   $226.66   $226.65   $226.70  
  Purchase #5 $186.66   5.710%   $197.3183   $197.32   $197.30   $197.30  
  Purchase #6 $213.59   9.117%   $233.063   $233.06   $233.05   $233.10  
  Purchase #7 $49.39   10.585%   $54.6179   $54.62   $54.60   $54.60  
  7 purchase totals = $965.65       $1,031.9132   $1,031.92   $1,031.85   $1,031.90