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	$231.92	4.613%	$242.6185	$242.62	$242.60	$242.60
Purchase #2	$238.85	8.512%	$259.1809	$259.18	$259.20	$259.20
Purchase #3	$48.60	5.158%	$51.1068	$51.11	$51.10	$51.10
Purchase #4	$203.77	3.346%	$210.5881	$210.59	$210.60	$210.60
Purchase #5	$49.73	10.351%	$54.8776	$54.88	$54.90	$54.90
Purchase #6	$28.84	12.628%	$32.4819	$32.48	$32.50	$32.50
Purchase #7	$71.90	6.300%	$76.4297	$76.43	$76.45	$76.40
7 purchase totals =	$873.61		$927.2835	$927.29	$927.35	$927.30