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 $153.42   9.649%   $168.2235   $168.22   $168.20   $168.20  
  Purchase #2 $161.99   13.726%   $184.2247   $184.22   $184.20   $184.20  
  Purchase #3 $89.45   13.822%   $101.8138   $101.81   $101.80   $101.80  
  Purchase #4 $98.27   9.828%   $107.928   $107.93   $107.95   $107.90  
  Purchase #5 $208.45   5.817%   $220.5755   $220.58   $220.60   $220.60  
  Purchase #6 $176.97   9.205%   $193.2601   $193.26   $193.25   $193.30  
  Purchase #7 $223.96   12.590%   $252.1566   $252.16   $252.15   $252.20  
  7 purchase totals = $1,112.51       $1,228.1822   $1,228.18   $1,228.15   $1,228.20