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	$54.51	9.317%	$59.5887	$59.59	$59.60	$59.60
Purchase #2	$10.75	6.128%	$11.4088	$11.41	$11.40	$11.40
Purchase #3	$56.43	10.423%	$62.3117	$62.31	$62.30	$62.30
Purchase #4	$138.65	4.775%	$145.2705	$145.27	$145.25	$145.30
Purchase #5	$15.73	5.869%	$16.6532	$16.65	$16.65	$16.70
Purchase #6	$107.34	3.814%	$111.4339	$111.43	$111.45	$111.40
Purchase #7	$162.86	5.467%	$171.7636	$171.76	$171.75	$171.80
7 purchase totals =	$546.27		$578.4304	$578.42	$578.40	$578.50