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 $85.36   10.389%   $94.2281   $94.23   $94.25   $94.20  
  Purchase #2 $48.54   6.728%   $51.8058   $51.81   $51.80   $51.80  
  Purchase #3 $248.84   9.414%   $272.2658   $272.27   $272.25   $272.30  
  Purchase #4 $201.81   9.779%   $221.545   $221.55   $221.55   $221.50  
  Purchase #5 $85.85   11.858%   $96.0301   $96.03   $96.05   $96.00  
  Purchase #6 $13.61   9.874%   $14.9539   $14.95   $14.95   $15.00  
  Purchase #7 $42.73   5.424%   $45.0477   $45.05   $45.05   $45.00  
  7 purchase totals = $726.74       $795.8764   $795.89   $795.90   $795.80