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 $208.50   13.355%   $236.3452   $236.35   $236.35   $236.30  
  Purchase #2 $148.41   3.558%   $153.6904   $153.69   $153.70   $153.70  
  Purchase #3 $158.44   9.420%   $173.365   $173.37   $173.35   $173.40  
  Purchase #4 $6.62   6.103%   $7.024   $7.02   $7.00   $7.00  
  Purchase #5 $151.31   6.407%   $161.0044   $161.00   $161.00   $161.00  
  Purchase #6 $24.75   8.608%   $26.8805   $26.88   $26.90   $26.90  
  Purchase #7 $91.51   7.696%   $98.5526   $98.55   $98.55   $98.60  
  7 purchase totals = $789.54       $856.8621   $856.86   $856.85   $856.90