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	$110.40	11.843%	$123.4747	$123.47	$123.45	$123.50
Purchase #2	$179.78	9.286%	$196.4744	$196.47	$196.45	$196.50
Purchase #3	$87.99	12.213%	$98.7362	$98.74	$98.75	$98.70
Purchase #4	$77.40	11.852%	$86.5734	$86.57	$86.55	$86.60
Purchase #5	$181.85	3.345%	$187.9329	$187.93	$187.95	$187.90
Purchase #6	$237.77	6.261%	$252.6568	$252.66	$252.65	$252.70
Purchase #7	$188.88	8.189%	$204.3474	$204.35	$204.35	$204.30
7 purchase totals =	$1,064.07		$1,150.1958	$1,150.19	$1,150.15	$1,150.20