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	$167.59	11.568%	$186.9768	$186.98	$187.00	$187.00
Purchase #2	$181.95	6.442%	$193.6712	$193.67	$193.65	$193.70
Purchase #3	$54.73	5.575%	$57.7812	$57.78	$57.80	$57.80
Purchase #4	$139.51	3.416%	$144.2757	$144.28	$144.30	$144.30
Purchase #5	$80.34	12.429%	$90.3255	$90.33	$90.35	$90.30
Purchase #6	$18.70	10.743%	$20.7089	$20.71	$20.70	$20.70
Purchase #7	$113.57	13.395%	$128.7827	$128.78	$128.80	$128.80
7 purchase totals =	$756.39		$822.5220	$822.53	$822.60	$822.60