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	$24.49	12.119%	$27.4579	$27.46	$27.45	$27.50
Purchase #2	$67.94	9.553%	$74.4303	$74.43	$74.45	$74.40
Purchase #3	$98.63	12.796%	$111.2507	$111.25	$111.25	$111.30
Purchase #4	$168.33	13.414%	$190.9098	$190.91	$190.90	$190.90
Purchase #5	$118.54	7.135%	$126.9978	$127.00	$127.00	$127.00
Purchase #6	$126.37	6.579%	$134.6839	$134.68	$134.70	$134.70
Purchase #7	$182.80	12.549%	$205.7396	$205.74	$205.75	$205.70
7 purchase totals =	$787.10		$871.4700	$871.47	$871.50	$871.50