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	$228.41	6.261%	$242.7108	$242.71	$242.70	$242.70
Purchase #2	$151.61	3.239%	$156.5206	$156.52	$156.50	$156.50
Purchase #3	$142.79	8.873%	$155.4598	$155.46	$155.45	$155.50
Purchase #4	$14.77	10.156%	$16.27	$16.27	$16.25	$16.30
Purchase #5	$234.73	7.111%	$251.4217	$251.42	$251.40	$251.40
Purchase #6	$79.25	13.431%	$89.8941	$89.89	$89.90	$89.90
Purchase #7	$217.78	13.470%	$247.115	$247.12	$247.10	$247.10
7 purchase totals =	$1,069.34		$1,159.3920	$1,159.39	$1,159.30	$1,159.40