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 $206.43   3.801%   $214.2764   $214.28   $214.30   $214.30  
  Purchase #2 $147.68   9.185%   $161.2444   $161.24   $161.25   $161.20  
  Purchase #3 $194.36   11.426%   $216.5676   $216.57   $216.55   $216.60  
  Purchase #4 $152.56   10.225%   $168.1593   $168.16   $168.15   $168.20  
  Purchase #5 $78.61   12.454%   $88.4001   $88.40   $88.40   $88.40  
  Purchase #6 $131.38   4.290%   $137.0162   $137.02   $137.00   $137.00  
  Purchase #7 $248.86   9.295%   $271.9915   $271.99   $272.00   $272.00  
  7 purchase totals = $1,159.88       $1,257.6555   $1,257.66   $1,257.65   $1,257.70