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 $183.87   13.266%   $208.2622   $208.26   $208.25   $208.30  
  Purchase #2 $155.51   10.712%   $172.1682   $172.17   $172.15   $172.20  
  Purchase #3 $60.83   8.789%   $66.1763   $66.18   $66.20   $66.20  
  Purchase #4 $190.55   13.692%   $216.6401   $216.64   $216.65   $216.60  
  Purchase #5 $159.31   11.871%   $178.2217   $178.22   $178.20   $178.20  
  Purchase #6 $137.34   12.431%   $154.4127   $154.41   $154.40   $154.40  
  Purchase #7 $66.36   5.393%   $69.9388   $69.94   $69.95   $69.90  
  7 purchase totals = $953.77       $1,065.8200   $1,065.82   $1,065.80   $1,065.80