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 $32.87   5.142%   $34.5602   $34.56   $34.55   $34.60  
  Purchase #2 $26.84   13.468%   $30.4548   $30.45   $30.45   $30.50  
  Purchase #3 $13.30   9.402%   $14.5505   $14.55   $14.55   $14.60  
  Purchase #4 $231.29   7.246%   $248.0493   $248.05   $248.05   $248.00  
  Purchase #5 $187.36   10.780%   $207.5574   $207.56   $207.55   $207.60  
  Purchase #6 $186.49   11.601%   $208.1247   $208.12   $208.10   $208.10  
  Purchase #7 $48.37   8.437%   $52.451   $52.45   $52.45   $52.50  
  7 purchase totals = $726.52       $795.7479   $795.74   $795.70   $795.90