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 $114.79   10.308%   $126.6226   $126.62   $126.60   $126.60  
  Purchase #2 $67.83   9.597%   $74.3396   $74.34   $74.35   $74.30  
  Purchase #3 $169.93   13.665%   $193.1509   $193.15   $193.15   $193.20  
  Purchase #4 $153.99   8.327%   $166.8127   $166.81   $166.80   $166.80  
  Purchase #5 $130.96   3.866%   $136.0229   $136.02   $136.00   $136.00  
  Purchase #6 $148.93   9.556%   $163.1618   $163.16   $163.15   $163.20  
  Purchase #7 $22.69   10.227%   $25.0105   $25.01   $25.00   $25.00  
  7 purchase totals = $809.12       $885.1210   $885.11   $885.05   $885.10