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	$179.97	13.842%	$204.8814	$204.88	$204.90	$204.90
Purchase #2	$120.85	6.274%	$128.4321	$128.43	$128.45	$128.40
Purchase #3	$226.88	12.193%	$254.5435	$254.54	$254.55	$254.50
Purchase #4	$188.75	6.291%	$200.6243	$200.62	$200.60	$200.60
Purchase #5	$73.45	13.367%	$83.2681	$83.27	$83.25	$83.30
Purchase #6	$29.32	4.586%	$30.6646	$30.66	$30.65	$30.70
Purchase #7	$93.52	12.563%	$105.2689	$105.27	$105.25	$105.30
7 purchase totals =	$912.74		$1,007.6829	$1,007.67	$1,007.65	$1,007.70