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 $96.64   6.865%   $103.2743   $103.27   $103.25   $103.30  
  Purchase #2 $33.41   3.747%   $34.6619   $34.66   $34.65   $34.70  
  Purchase #3 $17.43   8.631%   $18.9344   $18.93   $18.95   $18.90  
  Purchase #4 $231.41   4.748%   $242.3973   $242.40   $242.40   $242.40  
  Purchase #5 $118.58   13.103%   $134.1175   $134.12   $134.10   $134.10  
  Purchase #6 $175.60   5.463%   $185.193   $185.19   $185.20   $185.20  
  Purchase #7 $161.76   9.208%   $176.6549   $176.65   $176.65   $176.70  
  7 purchase totals = $834.83       $895.2333   $895.22   $895.20   $895.30