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 $226.91   3.233%   $234.246   $234.25   $234.25   $234.20  
  Purchase #2 $200.99   5.793%   $212.6334   $212.63   $212.65   $212.60  
  Purchase #3 $9.99   7.705%   $10.7597   $10.76   $10.75   $10.80  
  Purchase #4 $242.53   3.726%   $251.5667   $251.57   $251.55   $251.60  
  Purchase #5 $185.26   3.874%   $192.437   $192.44   $192.45   $192.40  
  Purchase #6 $159.41   3.251%   $164.5924   $164.59   $164.60   $164.60  
  Purchase #7 $84.37   7.824%   $90.9711   $90.97   $90.95   $91.00  
  7 purchase totals = $1,109.46       $1,157.2063   $1,157.21   $1,157.20   $1,157.20