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	$27.56	6.304%	$29.2974	$29.30	$29.30	$29.30
Purchase #2	$20.86	12.454%	$23.4579	$23.46	$23.45	$23.50
Purchase #3	$223.33	4.517%	$233.4178	$233.42	$233.40	$233.40
Purchase #4	$38.58	13.304%	$43.7127	$43.71	$43.70	$43.70
Purchase #5	$52.27	7.847%	$56.3716	$56.37	$56.35	$56.40
Purchase #6	$10.27	7.352%	$11.0251	$11.03	$11.05	$11.00
Purchase #7	$93.92	6.698%	$100.2108	$100.21	$100.20	$100.20
7 purchase totals =	$466.79		$497.4933	$497.50	$497.45	$497.50