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	$158.29	13.340%	$179.4059	$179.41	$179.40	$179.40
Purchase #2	$226.74	12.746%	$255.6403	$255.64	$255.65	$255.60
Purchase #3	$123.89	13.133%	$140.1605	$140.16	$140.15	$140.20
Purchase #4	$59.66	10.108%	$65.6904	$65.69	$65.70	$65.70
Purchase #5	$79.59	4.389%	$83.0832	$83.08	$83.10	$83.10
Purchase #6	$223.68	5.419%	$235.8012	$235.80	$235.80	$235.80
Purchase #7	$55.31	11.626%	$61.7403	$61.74	$61.75	$61.70
7 purchase totals =	$927.16		$1,021.5218	$1,021.52	$1,021.55	$1,021.50