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	$73.83	8.758%	$80.296	$80.30	$80.30	$80.30
Purchase #2	$31.32	11.231%	$34.8375	$34.84	$34.85	$34.80
Purchase #3	$195.65	13.275%	$221.6225	$221.62	$221.60	$221.60
Purchase #4	$63.49	4.398%	$66.2823	$66.28	$66.30	$66.30
Purchase #5	$249.98	10.144%	$275.338	$275.34	$275.35	$275.30
Purchase #6	$145.81	13.447%	$165.4171	$165.42	$165.40	$165.40
Purchase #7	$104.90	7.456%	$112.7213	$112.72	$112.70	$112.70
7 purchase totals =	$864.98		$956.5147	$956.52	$956.50	$956.40