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 $213.54   10.840%   $236.6877   $236.69   $236.70   $236.70  
  Purchase #2 $89.97   12.849%   $101.5302   $101.53   $101.55   $101.50  
  Purchase #3 $151.35   8.746%   $164.5871   $164.59   $164.60   $164.60  
  Purchase #4 $68.97   4.740%   $72.2392   $72.24   $72.25   $72.20  
  Purchase #5 $81.28   6.686%   $86.7144   $86.71   $86.70   $86.70  
  Purchase #6 $158.71   6.470%   $168.9785   $168.98   $169.00   $169.00  
  Purchase #7 $47.34   8.355%   $51.2953   $51.30   $51.30   $51.30  
  7 purchase totals = $811.16       $882.0324   $882.04   $882.10   $882.00