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	$157.71	9.452%	$172.6167	$172.62	$172.60	$172.60
Purchase #2	$42.94	6.244%	$45.6212	$45.62	$45.60	$45.60
Purchase #3	$211.53	10.475%	$233.6878	$233.69	$233.70	$233.70
Purchase #4	$131.26	12.662%	$147.8801	$147.88	$147.90	$147.90
Purchase #5	$139.97	7.767%	$150.8415	$150.84	$150.85	$150.80
Purchase #6	$42.65	3.520%	$44.1513	$44.15	$44.15	$44.20
Purchase #7	$166.79	7.513%	$179.3209	$179.32	$179.30	$179.30
7 purchase totals =	$892.85		$974.1195	$974.12	$974.10	$974.10