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 $235.37   13.274%   $266.613   $266.61   $266.60   $266.60  
  Purchase #2 $23.95   11.114%   $26.6118   $26.61   $26.60   $26.60  
  Purchase #3 $109.58   5.680%   $115.8041   $115.80   $115.80   $115.80  
  Purchase #4 $197.31   4.136%   $205.4707   $205.47   $205.45   $205.50  
  Purchase #5 $35.43   3.257%   $36.584   $36.58   $36.60   $36.60  
  Purchase #6 $56.26   3.661%   $58.3197   $58.32   $58.30   $58.30  
  Purchase #7 $15.45   9.351%   $16.8947   $16.89   $16.90   $16.90  
  7 purchase totals = $673.35       $726.2980   $726.28   $726.25   $726.30