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	$64.72	3.143%	$66.7541	$66.75	$66.75	$66.80
Purchase #2	$221.69	10.135%	$244.1583	$244.16	$244.15	$244.20
Purchase #3	$42.86	6.366%	$45.5885	$45.59	$45.60	$45.60
Purchase #4	$133.72	7.717%	$144.0392	$144.04	$144.05	$144.00
Purchase #5	$214.54	7.658%	$230.9695	$230.97	$230.95	$231.00
Purchase #6	$201.37	7.693%	$216.8614	$216.86	$216.85	$216.90
Purchase #7	$70.52	3.404%	$72.9205	$72.92	$72.90	$72.90
7 purchase totals =	$949.42		$1,021.2915	$1,021.29	$1,021.25	$1,021.40