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	$106.76	12.506%	$120.1114	$120.11	$120.10	$120.10
Purchase #2	$150.75	5.300%	$158.7398	$158.74	$158.75	$158.70
Purchase #3	$242.38	8.477%	$262.9266	$262.93	$262.95	$262.90
Purchase #4	$122.39	4.116%	$127.4276	$127.43	$127.45	$127.40
Purchase #5	$105.95	3.660%	$109.8278	$109.83	$109.85	$109.80
Purchase #6	$78.83	11.563%	$87.9451	$87.95	$87.95	$87.90
Purchase #7	$219.61	12.643%	$247.3753	$247.38	$247.40	$247.40
7 purchase totals =	$1,026.67		$1,114.3536	$1,114.37	$1,114.45	$1,114.20