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 $164.81   10.759%   $182.5419   $182.54   $182.55   $182.50  
  Purchase #2 $236.32   6.762%   $252.3   $252.30   $252.30   $252.30  
  Purchase #3 $225.57   6.344%   $239.8802   $239.88   $239.90   $239.90  
  Purchase #4 $116.92   12.193%   $131.1761   $131.18   $131.20   $131.20  
  Purchase #5 $127.50   6.273%   $135.4981   $135.50   $135.50   $135.50  
  Purchase #6 $195.39   9.237%   $213.4382   $213.44   $213.45   $213.40  
  Purchase #7 $53.66   5.246%   $56.475   $56.48   $56.50   $56.50  
  7 purchase totals = $1,120.17       $1,211.3095   $1,211.32   $1,211.40   $1,211.30