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	$247.84	12.324%	$278.3838	$278.38	$278.40	$278.40
Purchase #2	$58.32	7.551%	$62.7237	$62.72	$62.70	$62.70
Purchase #3	$119.28	3.247%	$123.153	$123.15	$123.15	$123.20
Purchase #4	$19.46	11.580%	$21.7135	$21.71	$21.70	$21.70
Purchase #5	$179.88	6.256%	$191.1333	$191.13	$191.15	$191.10
Purchase #6	$234.80	8.766%	$255.3826	$255.38	$255.40	$255.40
Purchase #7	$178.43	3.364%	$184.4324	$184.43	$184.45	$184.40
7 purchase totals =	$1,038.01		$1,116.9223	$1,116.90	$1,116.95	$1,116.90