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 $248.27   5.408%   $261.6964   $261.70   $261.70   $261.70  
  Purchase #2 $200.77   5.253%   $211.3164   $211.32   $211.30   $211.30  
  Purchase #3 $108.75   7.669%   $117.09   $117.09   $117.10   $117.10  
  Purchase #4 $133.88   8.261%   $144.9398   $144.94   $144.95   $144.90  
  Purchase #5 $244.71   9.631%   $268.278   $268.28   $268.30   $268.30  
  Purchase #6 $169.54   12.783%   $191.2123   $191.21   $191.20   $191.20  
  Purchase #7 $30.41   6.265%   $32.3152   $32.32   $32.30   $32.30  
  7 purchase totals = $1,136.33       $1,226.8481   $1,226.86   $1,226.85   $1,226.80