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 $53.89   8.755%   $58.6081   $58.61   $58.60   $58.60  
  Purchase #2 $221.42   4.831%   $232.1168   $232.12   $232.10   $232.10  
  Purchase #3 $216.77   10.451%   $239.4246   $239.42   $239.40   $239.40  
  Purchase #4 $133.37   10.125%   $146.8737   $146.87   $146.85   $146.90  
  Purchase #5 $185.46   12.346%   $208.3569   $208.36   $208.35   $208.40  
  Purchase #6 $190.89   13.377%   $216.4254   $216.43   $216.45   $216.40  
  Purchase #7 $114.59   11.532%   $127.8045   $127.80   $127.80   $127.80  
  7 purchase totals = $1,116.39       $1,229.6100   $1,229.61   $1,229.55   $1,229.60