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	$35.26	6.351%	$37.4994	$37.50	$37.50	$37.50
Purchase #2	$50.74	11.355%	$56.5015	$56.50	$56.50	$56.50
Purchase #3	$108.30	12.277%	$121.596	$121.60	$121.60	$121.60
Purchase #4	$76.69	12.222%	$86.0631	$86.06	$86.05	$86.10
Purchase #5	$43.40	5.363%	$45.7275	$45.73	$45.75	$45.70
Purchase #6	$104.38	6.621%	$111.291	$111.29	$111.30	$111.30
Purchase #7	$70.45	3.296%	$72.772	$72.77	$72.75	$72.80
7 purchase totals =	$489.22		$531.4505	$531.45	$531.45	$531.50