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	$79.31	13.194%	$89.7742	$89.77	$89.75	$89.80
Purchase #2	$171.30	10.419%	$189.1477	$189.15	$189.15	$189.10
Purchase #3	$215.79	11.549%	$240.7116	$240.71	$240.70	$240.70
Purchase #4	$146.83	7.371%	$157.6528	$157.65	$157.65	$157.70
Purchase #5	$181.32	13.229%	$205.3068	$205.31	$205.30	$205.30
Purchase #6	$17.73	13.853%	$20.1861	$20.19	$20.20	$20.20
Purchase #7	$74.70	4.233%	$77.8621	$77.86	$77.85	$77.90
7 purchase totals =	$886.98		$980.6413	$980.64	$980.60	$980.70