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 $241.62   9.863%   $265.451   $265.45   $265.45   $265.50  
  Purchase #2 $200.88   11.629%   $224.2403   $224.24   $224.25   $224.20  
  Purchase #3 $246.95   5.747%   $261.1422   $261.14   $261.15   $261.10  
  Purchase #4 $99.26   8.656%   $107.8519   $107.85   $107.85   $107.90  
  Purchase #5 $168.57   10.283%   $185.9041   $185.90   $185.90   $185.90  
  Purchase #6 $167.65   11.168%   $186.3732   $186.37   $186.35   $186.40  
  Purchase #7 $49.95   3.112%   $51.5044   $51.50   $51.50   $51.50  
  7 purchase totals = $1,174.88       $1,282.4671   $1,282.45   $1,282.45   $1,282.50