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	$78.25	10.278%	$86.2925	$86.29	$86.30	$86.30
Purchase #2	$48.66	13.280%	$55.122	$55.12	$55.10	$55.10
Purchase #3	$180.43	8.795%	$196.2988	$196.30	$196.30	$196.30
Purchase #4	$153.65	13.488%	$174.3743	$174.37	$174.35	$174.40
Purchase #5	$34.94	9.551%	$38.2771	$38.28	$38.30	$38.30
Purchase #6	$36.34	11.624%	$40.5642	$40.56	$40.55	$40.60
Purchase #7	$183.92	11.342%	$204.7802	$204.78	$204.80	$204.80
7 purchase totals =	$716.19		$795.7091	$795.70	$795.70	$795.80