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 $72.61   13.388%   $82.331   $82.33   $82.35   $82.30  
  Purchase #2 $130.33   8.412%   $141.2934   $141.29   $141.30   $141.30  
  Purchase #3 $177.81   13.268%   $201.4018   $201.40   $201.40   $201.40  
  Purchase #4 $235.30   7.199%   $252.2392   $252.24   $252.25   $252.20  
  Purchase #5 $47.60   8.425%   $51.6103   $51.61   $51.60   $51.60  
  Purchase #6 $48.70   11.866%   $54.4787   $54.48   $54.50   $54.50  
  Purchase #7 $233.62   12.564%   $262.972   $262.97   $262.95   $263.00  
  7 purchase totals = $945.97       $1,046.3264   $1,046.32   $1,046.35   $1,046.30