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	$96.97	6.321%	$103.0995	$103.10	$103.10	$103.10
Purchase #2	$157.30	6.121%	$166.9283	$166.93	$166.95	$166.90
Purchase #3	$95.65	4.677%	$100.1236	$100.12	$100.10	$100.10
Purchase #4	$48.75	8.839%	$53.059	$53.06	$53.05	$53.10
Purchase #5	$207.77	7.122%	$222.5674	$222.57	$222.55	$222.60
Purchase #6	$226.78	12.850%	$255.9212	$255.92	$255.90	$255.90
Purchase #7	$78.41	11.555%	$87.4703	$87.47	$87.45	$87.50
7 purchase totals =	$911.63		$989.1693	$989.17	$989.10	$989.20