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	$28.66	11.180%	$31.8642	$31.86	$31.85	$31.90
Purchase #2	$51.87	11.441%	$57.8044	$57.80	$57.80	$57.80
Purchase #3	$35.79	5.429%	$37.733	$37.73	$37.75	$37.70
Purchase #4	$226.53	5.131%	$238.1533	$238.15	$238.15	$238.20
Purchase #5	$64.57	9.243%	$70.5382	$70.54	$70.55	$70.50
Purchase #6	$106.39	5.725%	$112.4808	$112.48	$112.50	$112.50
Purchase #7	$12.33	5.652%	$13.0269	$13.03	$13.05	$13.00
7 purchase totals =	$526.14		$561.6008	$561.59	$561.65	$561.60