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	$246.42	4.803%	$258.2556	$258.26	$258.25	$258.30
Purchase #2	$91.72	10.759%	$101.5882	$101.59	$101.60	$101.60
Purchase #3	$149.39	3.457%	$154.5544	$154.55	$154.55	$154.60
Purchase #4	$34.93	11.169%	$38.8313	$38.83	$38.85	$38.80
Purchase #5	$223.78	11.195%	$248.8322	$248.83	$248.85	$248.80
Purchase #6	$97.66	3.405%	$100.9853	$100.99	$101.00	$101.00
Purchase #7	$234.70	6.450%	$249.8382	$249.84	$249.85	$249.80
7 purchase totals =	$1,078.60		$1,152.8852	$1,152.89	$1,152.95	$1,152.90