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	$14.76	10.274%	$16.2764	$16.28	$16.30	$16.30
Purchase #2	$201.69	10.452%	$222.7706	$222.77	$222.75	$222.80
Purchase #3	$214.56	7.558%	$230.7764	$230.78	$230.80	$230.80
Purchase #4	$196.94	9.757%	$216.1554	$216.16	$216.15	$216.20
Purchase #5	$111.85	10.334%	$123.4086	$123.41	$123.40	$123.40
Purchase #6	$204.30	5.612%	$215.7653	$215.77	$215.75	$215.80
Purchase #7	$194.78	11.665%	$217.5011	$217.50	$217.50	$217.50
7 purchase totals =	$1,138.88		$1,242.6538	$1,242.67	$1,242.65	$1,242.80