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	$49.29	9.720%	$54.081	$54.08	$54.10	$54.10
Purchase #2	$117.29	8.667%	$127.4555	$127.46	$127.45	$127.50
Purchase #3	$105.41	10.681%	$116.6688	$116.67	$116.65	$116.70
Purchase #4	$90.38	11.485%	$100.7601	$100.76	$100.75	$100.80
Purchase #5	$179.40	13.700%	$203.9778	$203.98	$204.00	$204.00
Purchase #6	$125.59	6.760%	$134.0799	$134.08	$134.10	$134.10
Purchase #7	$209.61	4.823%	$219.7195	$219.72	$219.70	$219.70
7 purchase totals =	$876.97		$956.7426	$956.75	$956.75	$956.90