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 $207.93   7.292%   $223.0923   $223.09   $223.10   $223.10  
  Purchase #2 $22.69   3.203%   $23.4168   $23.42   $23.40   $23.40  
  Purchase #3 $153.81   8.726%   $167.2315   $167.23   $167.25   $167.20  
  Purchase #4 $96.29   12.762%   $108.5785   $108.58   $108.60   $108.60  
  Purchase #5 $220.50   4.418%   $230.2417   $230.24   $230.25   $230.20  
  Purchase #6 $114.33   5.248%   $120.33   $120.33   $120.35   $120.30  
  Purchase #7 $23.72   10.490%   $26.2082   $26.21   $26.20   $26.20  
  7 purchase totals = $839.27       $899.0990   $899.10   $899.15   $899.00