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 $37.61   10.758%   $41.6561   $41.66   $41.65   $41.70  
  Purchase #2 $206.90   5.824%   $218.9499   $218.95   $218.95   $218.90  
  Purchase #3 $5.68   12.460%   $6.3877   $6.39   $6.40   $6.40  
  Purchase #4 $199.43   4.672%   $208.7474   $208.75   $208.75   $208.70  
  Purchase #5 $200.38   4.261%   $208.9182   $208.92   $208.90   $208.90  
  Purchase #6 $70.63   12.218%   $79.2596   $79.26   $79.25   $79.30  
  Purchase #7 $229.46   8.649%   $249.306   $249.31   $249.30   $249.30  
  7 purchase totals = $950.09       $1,013.2249   $1,013.24   $1,013.20   $1,013.20