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	$33.84	8.698%	$36.7834	$36.78	$36.80	$36.80
Purchase #2	$52.52	3.849%	$54.5415	$54.54	$54.55	$54.50
Purchase #3	$48.67	10.197%	$53.6329	$53.63	$53.65	$53.60
Purchase #4	$119.28	8.170%	$129.0252	$129.03	$129.05	$129.00
Purchase #5	$242.77	12.253%	$272.5166	$272.52	$272.50	$272.50
Purchase #6	$148.32	13.120%	$167.7796	$167.78	$167.80	$167.80
Purchase #7	$38.89	9.355%	$42.5282	$42.53	$42.55	$42.50
7 purchase totals =	$684.29		$756.8074	$756.81	$756.90	$756.70