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	$88.35	12.597%	$99.4794	$99.48	$99.50	$99.50
Purchase #2	$176.83	7.346%	$189.8199	$189.82	$189.80	$189.80
Purchase #3	$120.76	5.513%	$127.4175	$127.42	$127.40	$127.40
Purchase #4	$191.75	5.240%	$201.7977	$201.80	$201.80	$201.80
Purchase #5	$132.25	13.522%	$150.1328	$150.13	$150.15	$150.10
Purchase #6	$36.57	10.616%	$40.4523	$40.45	$40.45	$40.50
Purchase #7	$187.47	11.271%	$208.5997	$208.60	$208.60	$208.60
7 purchase totals =	$933.98		$1,017.6993	$1,017.70	$1,017.70	$1,017.70