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	$119.50	6.613%	$127.4025	$127.40	$127.40	$127.40
Purchase #2	$242.76	4.846%	$254.5241	$254.52	$254.50	$254.50
Purchase #3	$114.51	3.353%	$118.3495	$118.35	$118.35	$118.30
Purchase #4	$171.65	7.503%	$184.5289	$184.53	$184.55	$184.50
Purchase #5	$17.50	11.747%	$19.5557	$19.56	$19.55	$19.60
Purchase #6	$48.43	10.550%	$53.5394	$53.54	$53.55	$53.50
Purchase #7	$137.94	12.403%	$155.0487	$155.05	$155.05	$155.00
7 purchase totals =	$852.29		$912.9488	$912.95	$912.95	$912.80