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	$122.51	10.248%	$135.0648	$135.06	$135.05	$135.10
Purchase #2	$153.38	4.196%	$159.8158	$159.82	$159.80	$159.80
Purchase #3	$172.94	10.737%	$191.5086	$191.51	$191.50	$191.50
Purchase #4	$167.39	3.105%	$172.5875	$172.59	$172.60	$172.60
Purchase #5	$90.39	6.389%	$96.165	$96.17	$96.15	$96.20
Purchase #6	$101.88	7.520%	$109.5414	$109.54	$109.55	$109.50
Purchase #7	$241.97	13.339%	$274.2464	$274.25	$274.25	$274.20
7 purchase totals =	$1,050.46		$1,138.9295	$1,138.94	$1,138.90	$1,138.90