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	$215.69	3.449%	$223.1291	$223.13	$223.15	$223.10
Purchase #2	$250.95	13.773%	$285.5133	$285.51	$285.50	$285.50
Purchase #3	$226.61	13.176%	$256.4681	$256.47	$256.45	$256.50
Purchase #4	$5.89	6.505%	$6.2731	$6.27	$6.25	$6.30
Purchase #5	$166.40	3.846%	$172.7997	$172.80	$172.80	$172.80
Purchase #6	$152.63	9.362%	$166.9192	$166.92	$166.90	$166.90
Purchase #7	$159.92	5.832%	$169.2465	$169.25	$169.25	$169.20
7 purchase totals =	$1,178.09		$1,280.3490	$1,280.35	$1,280.30	$1,280.30