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	$50.56	9.408%	$55.3167	$55.32	$55.30	$55.30
Purchase #2	$103.43	5.856%	$109.4869	$109.49	$109.50	$109.50
Purchase #3	$116.83	11.570%	$130.3472	$130.35	$130.35	$130.30
Purchase #4	$59.86	4.653%	$62.6453	$62.65	$62.65	$62.60
Purchase #5	$154.62	7.155%	$165.6831	$165.68	$165.70	$165.70
Purchase #6	$62.98	4.690%	$65.9338	$65.93	$65.95	$65.90
Purchase #7	$239.61	13.262%	$271.3871	$271.39	$271.40	$271.40
7 purchase totals =	$787.89		$860.8001	$860.81	$860.85	$860.70