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 $169.41   8.608%   $183.9928   $183.99   $184.00   $184.00  
  Purchase #2 $246.75   7.491%   $265.234   $265.23   $265.25   $265.20  
  Purchase #3 $167.90   9.326%   $183.5584   $183.56   $183.55   $183.60  
  Purchase #4 $30.88   6.640%   $32.9304   $32.93   $32.95   $32.90  
  Purchase #5 $27.66   8.107%   $29.9024   $29.90   $29.90   $29.90  
  Purchase #6 $210.85   7.308%   $226.2589   $226.26   $226.25   $226.30  
  Purchase #7 $213.85   11.105%   $237.598   $237.60   $237.60   $237.60  
  7 purchase totals = $1,067.30       $1,159.4749   $1,159.47   $1,159.50   $1,159.50