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 $197.59   6.392%   $210.22   $210.22   $210.20   $210.20  
  Purchase #2 $225.27   13.497%   $255.6747   $255.67   $255.65   $255.70  
  Purchase #3 $105.86   3.328%   $109.383   $109.38   $109.40   $109.40  
  Purchase #4 $157.95   7.495%   $169.7884   $169.79   $169.80   $169.80  
  Purchase #5 $86.92   13.497%   $98.6516   $98.65   $98.65   $98.70  
  Purchase #6 $127.49   4.865%   $133.6924   $133.69   $133.70   $133.70  
  Purchase #7 $233.41   6.293%   $248.0985   $248.10   $248.10   $248.10  
  7 purchase totals = $1,134.49       $1,225.5086   $1,225.50   $1,225.50   $1,225.60