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	$56.70	10.482%	$62.6433	$62.64	$62.65	$62.60
Purchase #2	$138.95	3.135%	$143.3061	$143.31	$143.30	$143.30
Purchase #3	$190.83	4.275%	$198.988	$198.99	$199.00	$199.00
Purchase #4	$184.58	6.553%	$196.6755	$196.68	$196.70	$196.70
Purchase #5	$41.68	3.463%	$43.1234	$43.12	$43.10	$43.10
Purchase #6	$143.77	4.146%	$149.7307	$149.73	$149.75	$149.70
Purchase #7	$187.83	4.589%	$196.4495	$196.45	$196.45	$196.40
7 purchase totals =	$944.34		$990.9165	$990.92	$990.95	$990.80