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	$13.73	12.842%	$15.4932	$15.49	$15.50	$15.50
Purchase #2	$233.61	10.705%	$258.618	$258.62	$258.60	$258.60
Purchase #3	$212.81	8.228%	$230.32	$230.32	$230.30	$230.30
Purchase #4	$233.66	12.841%	$263.6643	$263.66	$263.65	$263.70
Purchase #5	$198.45	12.181%	$222.6232	$222.62	$222.60	$222.60
Purchase #6	$142.47	5.501%	$150.3073	$150.31	$150.30	$150.30
Purchase #7	$189.51	5.621%	$200.1624	$200.16	$200.15	$200.20
7 purchase totals =	$1,224.24		$1,341.1884	$1,341.18	$1,341.10	$1,341.20