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	$247.99	3.272%	$256.1042	$256.10	$256.10	$256.10
Purchase #2	$100.92	10.469%	$111.4853	$111.49	$111.50	$111.50
Purchase #3	$11.74	4.579%	$12.2776	$12.28	$12.30	$12.30
Purchase #4	$14.52	12.266%	$16.301	$16.30	$16.30	$16.30
Purchase #5	$115.37	10.366%	$127.3293	$127.33	$127.35	$127.30
Purchase #6	$76.59	6.691%	$81.7146	$81.71	$81.70	$81.70
Purchase #7	$187.31	9.715%	$205.5072	$205.51	$205.50	$205.50
7 purchase totals =	$754.44		$810.7192	$810.72	$810.75	$810.70