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	$48.99	3.753%	$50.8286	$50.83	$50.85	$50.80
Purchase #2	$226.83	11.790%	$253.5733	$253.57	$253.55	$253.60
Purchase #3	$57.70	7.119%	$61.8077	$61.81	$61.80	$61.80
Purchase #4	$202.39	10.262%	$223.1593	$223.16	$223.15	$223.20
Purchase #5	$147.26	7.643%	$158.5151	$158.52	$158.50	$158.50
Purchase #6	$63.60	13.442%	$72.1491	$72.15	$72.15	$72.10
Purchase #7	$32.54	10.723%	$36.0293	$36.03	$36.05	$36.00
7 purchase totals =	$779.31		$856.0624	$856.07	$856.05	$856.00