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	$12.31	4.535%	$12.8683	$12.87	$12.85	$12.90
Purchase #2	$190.56	7.169%	$204.2212	$204.22	$204.20	$204.20
Purchase #3	$218.33	6.784%	$233.1415	$233.14	$233.15	$233.10
Purchase #4	$67.91	13.273%	$76.9237	$76.92	$76.90	$76.90
Purchase #5	$5.55	9.142%	$6.0574	$6.06	$6.05	$6.10
Purchase #6	$7.25	4.644%	$7.5867	$7.59	$7.60	$7.60
Purchase #7	$233.59	4.658%	$244.4706	$244.47	$244.45	$244.50
7 purchase totals =	$735.50		$785.2694	$785.27	$785.20	$785.30