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 $248.60   7.123%   $266.3078   $266.31   $266.30   $266.30  
  Purchase #2 $206.51   4.250%   $215.2867   $215.29   $215.30   $215.30  
  Purchase #3 $236.63   7.495%   $254.3654   $254.37   $254.35   $254.40  
  Purchase #4 $122.38   7.281%   $131.2905   $131.29   $131.30   $131.30  
  Purchase #5 $182.88   4.798%   $191.6546   $191.65   $191.65   $191.70  
  Purchase #6 $58.41   3.271%   $60.3206   $60.32   $60.30   $60.30  
  Purchase #7 $140.30   12.246%   $157.4811   $157.48   $157.50   $157.50  
  7 purchase totals = $1,195.71       $1,276.7067   $1,276.71   $1,276.70   $1,276.80