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 $67.73   9.689%   $74.2924   $74.29   $74.30   $74.30  
  Purchase #2 $173.68   13.258%   $196.7065   $196.71   $196.70   $196.70  
  Purchase #3 $164.69   12.450%   $185.1939   $185.19   $185.20   $185.20  
  Purchase #4 $241.87   5.319%   $254.7351   $254.74   $254.75   $254.70  
  Purchase #5 $27.58   9.392%   $30.1703   $30.17   $30.15   $30.20  
  Purchase #6 $106.65   7.802%   $114.9708   $114.97   $114.95   $115.00  
  Purchase #7 $35.87   9.440%   $39.2561   $39.26   $39.25   $39.30  
  7 purchase totals = $818.07       $895.3251   $895.33   $895.30   $895.40