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 $124.97   11.339%   $139.1403   $139.14   $139.15   $139.10  
  Purchase #2 $164.45   7.417%   $176.6473   $176.65   $176.65   $176.60  
  Purchase #3 $116.58   8.243%   $126.1897   $126.19   $126.20   $126.20  
  Purchase #4 $18.96   12.139%   $21.2616   $21.26   $21.25   $21.30  
  Purchase #5 $123.41   5.617%   $130.3419   $130.34   $130.35   $130.30  
  Purchase #6 $207.71   12.653%   $233.9915   $233.99   $234.00   $234.00  
  Purchase #7 $182.70   13.627%   $207.5965   $207.60   $207.60   $207.60  
  7 purchase totals = $938.78       $1,035.1688   $1,035.17   $1,035.20   $1,035.10