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	$75.35	4.844%	$79	$79.00	$79.00	$79.00
Purchase #2	$246.68	3.584%	$255.521	$255.52	$255.50	$255.50
Purchase #3	$122.77	3.679%	$127.2867	$127.29	$127.30	$127.30
Purchase #4	$173.35	7.291%	$185.9889	$185.99	$186.00	$186.00
Purchase #5	$222.46	12.873%	$251.0973	$251.10	$251.10	$251.10
Purchase #6	$54.26	9.310%	$59.3116	$59.31	$59.30	$59.30
Purchase #7	$51.39	11.337%	$57.2161	$57.22	$57.20	$57.20
7 purchase totals =	$946.26		$1,015.4216	$1,015.43	$1,015.40	$1,015.40