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	$104.47	6.612%	$111.3776	$111.38	$111.40	$111.40
Purchase #2	$17.31	10.323%	$19.0969	$19.10	$19.10	$19.10
Purchase #3	$116.50	13.750%	$132.5188	$132.52	$132.50	$132.50
Purchase #4	$229.73	7.612%	$247.217	$247.22	$247.20	$247.20
Purchase #5	$164.28	7.352%	$176.3579	$176.36	$176.35	$176.40
Purchase #6	$109.33	6.866%	$116.8366	$116.84	$116.85	$116.80
Purchase #7	$49.32	13.244%	$55.8519	$55.85	$55.85	$55.90
7 purchase totals =	$790.94		$859.2567	$859.27	$859.25	$859.30