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	$249.98	13.843%	$284.5847	$284.58	$284.60	$284.60
Purchase #2	$138.82	8.685%	$150.8765	$150.88	$150.90	$150.90
Purchase #3	$157.76	3.305%	$162.974	$162.97	$162.95	$163.00
Purchase #4	$111.57	11.243%	$124.1138	$124.11	$124.10	$124.10
Purchase #5	$250.40	13.227%	$283.5204	$283.52	$283.50	$283.50
Purchase #6	$115.58	13.621%	$131.3232	$131.32	$131.30	$131.30
Purchase #7	$6.71	4.277%	$6.997	$7.00	$7.00	$7.00
7 purchase totals =	$1,030.82		$1,144.3896	$1,144.38	$1,144.35	$1,144.40