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 $102.63   8.341%   $111.1904   $111.19   $111.20   $111.20  
  Purchase #2 $137.51   10.851%   $152.4312   $152.43   $152.45   $152.40  
  Purchase #3 $69.34   10.683%   $76.7476   $76.75   $76.75   $76.70  
  Purchase #4 $179.64   3.445%   $185.8286   $185.83   $185.85   $185.80  
  Purchase #5 $101.36   12.482%   $114.0118   $114.01   $114.00   $114.00  
  Purchase #6 $237.55   13.321%   $269.194   $269.19   $269.20   $269.20  
  Purchase #7 $176.74   10.327%   $194.9919   $194.99   $195.00   $195.00  
  7 purchase totals = $1,004.77       $1,104.3955   $1,104.39   $1,104.45   $1,104.30