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	$100.54	6.535%	$107.1103	$107.11	$107.10	$107.10
Purchase #2	$142.82	11.200%	$158.8158	$158.82	$158.80	$158.80
Purchase #3	$43.31	13.683%	$49.2361	$49.24	$49.25	$49.20
Purchase #4	$192.29	13.677%	$218.5895	$218.59	$218.60	$218.60
Purchase #5	$94.29	11.557%	$105.1871	$105.19	$105.20	$105.20
Purchase #6	$80.59	6.422%	$85.7655	$85.77	$85.75	$85.80
Purchase #7	$62.79	13.764%	$71.4324	$71.43	$71.45	$71.40
7 purchase totals =	$716.63		$796.1367	$796.15	$796.15	$796.10