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	$12.33	11.463%	$13.7434	$13.74	$13.75	$13.70
Purchase #2	$51.87	5.678%	$54.8152	$54.82	$54.80	$54.80
Purchase #3	$92.48	8.825%	$100.6414	$100.64	$100.65	$100.60
Purchase #4	$158.27	13.429%	$179.5241	$179.52	$179.50	$179.50
Purchase #5	$151.90	10.233%	$167.4439	$167.44	$167.45	$167.40
Purchase #6	$151.66	10.482%	$167.557	$167.56	$167.55	$167.60
Purchase #7	$103.57	3.173%	$106.8563	$106.86	$106.85	$106.90
7 purchase totals =	$722.08		$790.5813	$790.58	$790.55	$790.50