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	$20.77	6.466%	$22.113	$22.11	$22.10	$22.10
Purchase #2	$46.54	12.636%	$52.4208	$52.42	$52.40	$52.40
Purchase #3	$52.56	5.113%	$55.2474	$55.25	$55.25	$55.20
Purchase #4	$185.84	10.157%	$204.7158	$204.72	$204.70	$204.70
Purchase #5	$88.98	3.330%	$91.943	$91.94	$91.95	$91.90
Purchase #6	$18.27	4.278%	$19.0516	$19.05	$19.05	$19.10
Purchase #7	$206.60	6.399%	$219.8203	$219.82	$219.80	$219.80
7 purchase totals =	$619.56		$665.3119	$665.31	$665.25	$665.20