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 $168.31   11.210%   $187.1776   $187.18   $187.20   $187.20  
  Purchase #2 $236.77   12.538%   $266.4562   $266.46   $266.45   $266.50  
  Purchase #3 $23.83   11.663%   $26.6093   $26.61   $26.60   $26.60  
  Purchase #4 $131.63   8.591%   $142.9383   $142.94   $142.95   $142.90  
  Purchase #5 $177.37   6.843%   $189.5074   $189.51   $189.50   $189.50  
  Purchase #6 $240.99   9.490%   $263.86   $263.86   $263.85   $263.90  
  Purchase #7 $236.47   7.714%   $254.7113   $254.71   $254.70   $254.70  
  7 purchase totals = $1,215.37       $1,331.2601   $1,331.27   $1,331.25   $1,331.30