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 $112.37   6.616%   $119.8044   $119.80   $119.80   $119.80  
  Purchase #2 $84.95   13.573%   $96.4803   $96.48   $96.50   $96.50  
  Purchase #3 $156.89   8.172%   $169.7111   $169.71   $169.70   $169.70  
  Purchase #4 $231.30   7.720%   $249.1564   $249.16   $249.15   $249.20  
  Purchase #5 $34.76   9.799%   $38.1661   $38.17   $38.15   $38.20  
  Purchase #6 $102.69   3.161%   $105.936   $105.94   $105.95   $105.90  
  Purchase #7 $246.35   7.634%   $265.1564   $265.16   $265.15   $265.20  
  7 purchase totals = $969.31       $1,044.4107   $1,044.42   $1,044.40   $1,044.50