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	$53.42	9.280%	$58.3774	$58.38	$58.40	$58.40
Purchase #2	$15.80	9.622%	$17.3203	$17.32	$17.30	$17.30
Purchase #3	$94.47	11.698%	$105.5211	$105.52	$105.50	$105.50
Purchase #4	$50.95	6.196%	$54.1069	$54.11	$54.10	$54.10
Purchase #5	$158.48	8.872%	$172.5403	$172.54	$172.55	$172.50
Purchase #6	$34.28	12.157%	$38.4474	$38.45	$38.45	$38.40
Purchase #7	$79.36	4.761%	$83.1383	$83.14	$83.15	$83.10
7 purchase totals =	$486.76		$529.4517	$529.46	$529.45	$529.30