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	$150.28	5.731%	$158.8925	$158.89	$158.90	$158.90
Purchase #2	$159.67	6.869%	$170.6377	$170.64	$170.65	$170.60
Purchase #3	$62.55	9.502%	$68.4935	$68.49	$68.50	$68.50
Purchase #4	$39.89	12.287%	$44.7913	$44.79	$44.80	$44.80
Purchase #5	$64.92	12.239%	$72.8656	$72.87	$72.85	$72.90
Purchase #6	$79.37	4.391%	$82.8551	$82.86	$82.85	$82.90
Purchase #7	$22.56	13.395%	$25.5819	$25.58	$25.60	$25.60
7 purchase totals =	$579.24		$624.1176	$624.12	$624.15	$624.20