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 $53.70   12.173%   $60.2369   $60.24   $60.25   $60.20  
  Purchase #2 $221.55   13.624%   $251.734   $251.73   $251.75   $251.70  
  Purchase #3 $213.89   12.345%   $240.2947   $240.29   $240.30   $240.30  
  Purchase #4 $223.58   7.302%   $239.9058   $239.91   $239.90   $239.90  
  Purchase #5 $182.45   5.285%   $192.0925   $192.09   $192.10   $192.10  
  Purchase #6 $191.64   13.269%   $217.0687   $217.07   $217.05   $217.10  
  Purchase #7 $210.25   11.188%   $233.7728   $233.77   $233.75   $233.80  
  7 purchase totals = $1,297.06       $1,435.1054   $1,435.10   $1,435.10   $1,435.10