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	$51.82	12.681%	$58.3913	$58.39	$58.40	$58.40
Purchase #2	$204.27	6.275%	$217.0879	$217.09	$217.10	$217.10
Purchase #3	$172.57	8.553%	$187.3299	$187.33	$187.35	$187.30
Purchase #4	$56.83	9.828%	$62.4153	$62.42	$62.40	$62.40
Purchase #5	$156.57	5.653%	$165.4209	$165.42	$165.40	$165.40
Purchase #6	$18.35	4.419%	$19.1609	$19.16	$19.15	$19.20
Purchase #7	$139.31	5.240%	$146.6098	$146.61	$146.60	$146.60
7 purchase totals =	$799.72		$856.4160	$856.42	$856.40	$856.40