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	$250.70	8.607%	$272.2777	$272.28	$272.30	$272.30
Purchase #2	$188.57	11.719%	$210.6685	$210.67	$210.65	$210.70
Purchase #3	$31.95	4.591%	$33.4168	$33.42	$33.40	$33.40
Purchase #4	$126.86	9.673%	$139.1312	$139.13	$139.15	$139.10
Purchase #5	$150.99	6.312%	$160.5205	$160.52	$160.50	$160.50
Purchase #6	$93.59	7.351%	$100.4698	$100.47	$100.45	$100.50
Purchase #7	$102.87	6.103%	$109.1482	$109.15	$109.15	$109.10
7 purchase totals =	$945.53		$1,025.6327	$1,025.64	$1,025.60	$1,025.60