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	$39.34	7.437%	$42.2657	$42.27	$42.25	$42.30
Purchase #2	$63.31	11.507%	$70.5951	$70.60	$70.60	$70.60
Purchase #3	$38.27	11.323%	$42.6033	$42.60	$42.60	$42.60
Purchase #4	$111.73	9.750%	$122.6237	$122.62	$122.60	$122.60
Purchase #5	$168.43	6.337%	$179.1034	$179.10	$179.10	$179.10
Purchase #6	$66.45	13.225%	$75.238	$75.24	$75.25	$75.20
Purchase #7	$132.69	10.643%	$146.8122	$146.81	$146.80	$146.80
7 purchase totals =	$620.22		$679.2414	$679.24	$679.20	$679.20