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	$48.39	4.257%	$50.45	$50.45	$50.45	$50.50
Purchase #2	$15.61	3.322%	$16.1286	$16.13	$16.15	$16.10
Purchase #3	$9.57	13.338%	$10.8464	$10.85	$10.85	$10.80
Purchase #4	$90.64	8.453%	$98.3018	$98.30	$98.30	$98.30
Purchase #5	$191.89	3.440%	$198.491	$198.49	$198.50	$198.50
Purchase #6	$70.33	6.783%	$75.1005	$75.10	$75.10	$75.10
Purchase #7	$181.41	4.810%	$190.1358	$190.14	$190.15	$190.10
7 purchase totals =	$607.84		$639.4541	$639.46	$639.50	$639.40