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 $159.53   8.563%   $173.1906   $173.19   $173.20   $173.20  
  Purchase #2 $119.68   12.366%   $134.4796   $134.48   $134.50   $134.50  
  Purchase #3 $48.64   10.552%   $53.7725   $53.77   $53.75   $53.80  
  Purchase #4 $116.76   11.552%   $130.2481   $130.25   $130.25   $130.20  
  Purchase #5 $62.29   8.466%   $67.5635   $67.56   $67.55   $67.60  
  Purchase #6 $95.93   11.602%   $107.0598   $107.06   $107.05   $107.10  
  Purchase #7 $30.27   6.627%   $32.276   $32.28   $32.30   $32.30  
  7 purchase totals = $633.10       $698.5901   $698.59   $698.60   $698.70