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 $91.42   5.868%   $96.7845   $96.78   $96.80   $96.80  
  Purchase #2 $78.97   10.129%   $86.9689   $86.97   $86.95   $87.00  
  Purchase #3 $202.60   4.549%   $211.8163   $211.82   $211.80   $211.80  
  Purchase #4 $141.29   11.132%   $157.0184   $157.02   $157.00   $157.00  
  Purchase #5 $141.58   9.248%   $154.6733   $154.67   $154.65   $154.70  
  Purchase #6 $154.82   4.155%   $161.2528   $161.25   $161.25   $161.30  
  Purchase #7 $91.68   7.339%   $98.4084   $98.41   $98.40   $98.40  
  7 purchase totals = $902.36       $966.9226   $966.92   $966.85   $967.00