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	$164.32	8.628%	$178.4975	$178.50	$178.50	$178.50
Purchase #2	$173.64	12.119%	$194.6834	$194.68	$194.70	$194.70
Purchase #3	$238.31	11.621%	$266.004	$266.00	$266.00	$266.00
Purchase #4	$173.57	9.842%	$190.6528	$190.65	$190.65	$190.70
Purchase #5	$58.34	4.591%	$61.0184	$61.02	$61.00	$61.00
Purchase #6	$226.72	10.485%	$250.4916	$250.49	$250.50	$250.50
Purchase #7	$146.67	13.778%	$166.8782	$166.88	$166.90	$166.90
7 purchase totals =	$1,181.57		$1,308.2259	$1,308.22	$1,308.25	$1,308.30