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	$222.62	12.551%	$250.561	$250.56	$250.55	$250.60
Purchase #2	$44.65	8.659%	$48.5162	$48.52	$48.50	$48.50
Purchase #3	$9.98	4.303%	$10.4094	$10.41	$10.40	$10.40
Purchase #4	$98.50	13.253%	$111.5542	$111.55	$111.55	$111.60
Purchase #5	$163.41	13.510%	$185.4867	$185.49	$185.50	$185.50
Purchase #6	$22.96	11.615%	$25.6268	$25.63	$25.65	$25.60
Purchase #7	$18.93	4.531%	$19.7877	$19.79	$19.80	$19.80
7 purchase totals =	$581.05		$651.9420	$651.95	$651.95	$652.00