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 $228.56   13.122%   $258.5516   $258.55   $258.55   $258.60  
  Purchase #2 $198.57   4.168%   $206.8464   $206.85   $206.85   $206.80  
  Purchase #3 $20.86   10.569%   $23.0647   $23.06   $23.05   $23.10  
  Purchase #4 $177.32   4.492%   $185.2852   $185.29   $185.30   $185.30  
  Purchase #5 $209.55   4.439%   $218.8519   $218.85   $218.85   $218.90  
  Purchase #6 $165.63   5.206%   $174.2527   $174.25   $174.25   $174.30  
  Purchase #7 $244.98   7.107%   $262.3907   $262.39   $262.40   $262.40  
  7 purchase totals = $1,245.47       $1,329.2432   $1,329.24   $1,329.25   $1,329.40