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	$17.80	4.401%	$18.5834	$18.58	$18.60	$18.60
Purchase #2	$146.54	4.564%	$153.2281	$153.23	$153.25	$153.20
Purchase #3	$113.39	4.515%	$118.5096	$118.51	$118.50	$118.50
Purchase #4	$229.32	5.257%	$241.3754	$241.38	$241.40	$241.40
Purchase #5	$6.67	13.830%	$7.5925	$7.59	$7.60	$7.60
Purchase #6	$105.80	7.505%	$113.7403	$113.74	$113.75	$113.70
Purchase #7	$72.50	9.710%	$79.5398	$79.54	$79.55	$79.50
7 purchase totals =	$692.02		$732.5691	$732.57	$732.65	$732.50