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	$246.60	3.215%	$254.5282	$254.53	$254.55	$254.50
Purchase #2	$64.34	10.773%	$71.2713	$71.27	$71.25	$71.30
Purchase #3	$18.70	9.129%	$20.4071	$20.41	$20.40	$20.40
Purchase #4	$21.65	13.313%	$24.5323	$24.53	$24.55	$24.50
Purchase #5	$31.31	12.451%	$35.2084	$35.21	$35.20	$35.20
Purchase #6	$19.46	5.307%	$20.4927	$20.49	$20.50	$20.50
Purchase #7	$228.44	10.246%	$251.846	$251.85	$251.85	$251.80
7 purchase totals =	$630.50		$678.2860	$678.29	$678.30	$678.20