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	$79.51	13.198%	$90.0037	$90.00	$90.00	$90.00
Purchase #2	$19.88	12.649%	$22.3946	$22.39	$22.40	$22.40
Purchase #3	$121.85	5.640%	$128.7223	$128.72	$128.70	$128.70
Purchase #4	$46.41	5.268%	$48.8549	$48.85	$48.85	$48.90
Purchase #5	$100.83	4.573%	$105.441	$105.44	$105.45	$105.40
Purchase #6	$86.43	5.579%	$91.2519	$91.25	$91.25	$91.30
Purchase #7	$198.50	13.115%	$224.5333	$224.53	$224.55	$224.50
7 purchase totals =	$653.41		$711.2017	$711.18	$711.20	$711.20