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 $86.63   13.762%   $98.552   $98.55   $98.55   $98.60  
  Purchase #2 $29.99   5.675%   $31.6919   $31.69   $31.70   $31.70  
  Purchase #3 $218.48   9.802%   $239.8954   $239.90   $239.90   $239.90  
  Purchase #4 $66.42   11.712%   $74.1991   $74.20   $74.20   $74.20  
  Purchase #5 $86.97   12.733%   $98.0439   $98.04   $98.05   $98.00  
  Purchase #6 $154.57   5.551%   $163.1502   $163.15   $163.15   $163.20  
  Purchase #7 $225.64   13.298%   $255.6456   $255.65   $255.65   $255.60  
  7 purchase totals = $868.70       $961.1781   $961.18   $961.20   $961.20