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	$63.48	3.596%	$65.7627	$65.76	$65.75	$65.80
Purchase #2	$90.69	10.176%	$99.9186	$99.92	$99.90	$99.90
Purchase #3	$228.83	11.373%	$254.8548	$254.85	$254.85	$254.90
Purchase #4	$46.84	12.414%	$52.6547	$52.65	$52.65	$52.70
Purchase #5	$165.71	4.692%	$173.4851	$173.49	$173.50	$173.50
Purchase #6	$139.72	9.822%	$153.4433	$153.44	$153.45	$153.40
Purchase #7	$162.95	9.475%	$178.3895	$178.39	$178.40	$178.40
7 purchase totals =	$898.22		$978.5087	$978.50	$978.50	$978.60