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	$27.48	5.204%	$28.9101	$28.91	$28.90	$28.90
Purchase #2	$108.83	12.226%	$122.1356	$122.14	$122.15	$122.10
Purchase #3	$48.34	13.594%	$54.9113	$54.91	$54.90	$54.90
Purchase #4	$229.59	4.411%	$239.7172	$239.72	$239.70	$239.70
Purchase #5	$153.94	8.166%	$166.5107	$166.51	$166.50	$166.50
Purchase #6	$235.38	3.224%	$242.9687	$242.97	$242.95	$243.00
Purchase #7	$195.48	13.730%	$222.3194	$222.32	$222.30	$222.30
7 purchase totals =	$999.04		$1,077.4730	$1,077.48	$1,077.40	$1,077.40