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	$11.84	6.287%	$12.5844	$12.58	$12.60	$12.60
Purchase #2	$188.40	10.631%	$208.4288	$208.43	$208.45	$208.40
Purchase #3	$229.61	11.740%	$256.5662	$256.57	$256.55	$256.60
Purchase #4	$216.39	11.449%	$241.1645	$241.16	$241.15	$241.20
Purchase #5	$212.33	6.230%	$225.5582	$225.56	$225.55	$225.60
Purchase #6	$34.52	12.470%	$38.8246	$38.82	$38.80	$38.80
Purchase #7	$122.69	5.300%	$129.1926	$129.19	$129.20	$129.20
7 purchase totals =	$1,015.78		$1,112.3193	$1,112.31	$1,112.30	$1,112.40