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	$108.67	10.652%	$120.2455	$120.25	$120.25	$120.20
Purchase #2	$173.70	6.404%	$184.8237	$184.82	$184.80	$184.80
Purchase #3	$115.41	6.649%	$123.0836	$123.08	$123.10	$123.10
Purchase #4	$247.91	12.596%	$279.1367	$279.14	$279.15	$279.10
Purchase #5	$187.52	4.588%	$196.1234	$196.12	$196.10	$196.10
Purchase #6	$219.30	12.774%	$247.3134	$247.31	$247.30	$247.30
Purchase #7	$16.69	7.170%	$17.8867	$17.89	$17.90	$17.90
7 purchase totals =	$1,069.20		$1,168.6130	$1,168.61	$1,168.60	$1,168.50