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	$129.85	11.209%	$144.4049	$144.40	$144.40	$144.40
Purchase #2	$6.68	6.461%	$7.1116	$7.11	$7.10	$7.10
Purchase #3	$165.25	4.305%	$172.364	$172.36	$172.35	$172.40
Purchase #4	$52.29	8.815%	$56.8994	$56.90	$56.90	$56.90
Purchase #5	$11.86	8.398%	$12.856	$12.86	$12.85	$12.90
Purchase #6	$218.94	12.158%	$245.5587	$245.56	$245.55	$245.60
Purchase #7	$40.29	10.496%	$44.5188	$44.52	$44.50	$44.50
7 purchase totals =	$625.16		$683.7134	$683.71	$683.65	$683.80