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 $181.54   11.649%   $202.6876   $202.69   $202.70   $202.70  
  Purchase #2 $116.77   10.212%   $128.6946   $128.69   $128.70   $128.70  
  Purchase #3 $161.58   13.302%   $183.0734   $183.07   $183.05   $183.10  
  Purchase #4 $32.76   3.825%   $34.0131   $34.01   $34.00   $34.00  
  Purchase #5 $101.90   9.211%   $111.286   $111.29   $111.30   $111.30  
  Purchase #6 $196.75   9.515%   $215.4708   $215.47   $215.45   $215.50  
  Purchase #7 $125.65   4.195%   $130.921   $130.92   $130.90   $130.90  
  7 purchase totals = $916.95       $1,006.1465   $1,006.14   $1,006.10   $1,006.20