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	$142.37	13.247%	$161.2298	$161.23	$161.25	$161.20
Purchase #2	$80.38	12.150%	$90.1462	$90.15	$90.15	$90.10
Purchase #3	$12.87	13.172%	$14.5652	$14.57	$14.55	$14.60
Purchase #4	$105.58	10.589%	$116.7599	$116.76	$116.75	$116.80
Purchase #5	$38.84	7.257%	$41.6586	$41.66	$41.65	$41.70
Purchase #6	$146.27	4.712%	$153.1622	$153.16	$153.15	$153.20
Purchase #7	$88.48	13.324%	$100.2691	$100.27	$100.25	$100.30
7 purchase totals =	$614.79		$677.7910	$677.80	$677.75	$677.90