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	$92.89	6.608%	$99.0282	$99.03	$99.05	$99.00
Purchase #2	$42.25	12.575%	$47.5629	$47.56	$47.55	$47.60
Purchase #3	$149.64	10.853%	$165.8804	$165.88	$165.90	$165.90
Purchase #4	$214.35	8.130%	$231.7767	$231.78	$231.80	$231.80
Purchase #5	$153.70	12.199%	$172.4499	$172.45	$172.45	$172.40
Purchase #6	$100.45	5.354%	$105.8281	$105.83	$105.85	$105.80
Purchase #7	$64.52	10.810%	$71.4946	$71.49	$71.50	$71.50
7 purchase totals =	$817.80		$894.0208	$894.02	$894.10	$894.00