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 $223.69   13.226%   $253.2752   $253.28   $253.30   $253.30  
  Purchase #2 $192.64   7.371%   $206.8395   $206.84   $206.85   $206.80  
  Purchase #3 $127.80   4.103%   $133.0436   $133.04   $133.05   $133.00  
  Purchase #4 $117.99   12.819%   $133.1151   $133.12   $133.10   $133.10  
  Purchase #5 $115.74   13.624%   $131.5084   $131.51   $131.50   $131.50  
  Purchase #6 $34.33   3.236%   $35.4409   $35.44   $35.45   $35.40  
  Purchase #7 $242.50   4.202%   $252.6899   $252.69   $252.70   $252.70  
  7 purchase totals = $1,054.69       $1,145.9126   $1,145.92   $1,145.95   $1,145.80