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	$49.30	3.275%	$50.9146	$50.91	$50.90	$50.90
Purchase #2	$62.93	8.533%	$68.2998	$68.30	$68.30	$68.30
Purchase #3	$83.72	7.456%	$89.9622	$89.96	$89.95	$90.00
Purchase #4	$167.56	6.543%	$178.5235	$178.52	$178.50	$178.50
Purchase #5	$56.62	7.194%	$60.6932	$60.69	$60.70	$60.70
Purchase #6	$190.76	3.262%	$196.9826	$196.98	$197.00	$197.00
Purchase #7	$105.43	5.602%	$111.3362	$111.34	$111.35	$111.30
7 purchase totals =	$716.32		$756.7121	$756.70	$756.70	$756.70