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	$111.72	6.196%	$118.6422	$118.64	$118.65	$118.60
Purchase #2	$214.61	12.598%	$241.6466	$241.65	$241.65	$241.60
Purchase #3	$215.92	5.265%	$227.2882	$227.29	$227.30	$227.30
Purchase #4	$199.73	4.194%	$208.1067	$208.11	$208.10	$208.10
Purchase #5	$84.38	6.685%	$90.0208	$90.02	$90.00	$90.00
Purchase #6	$144.88	3.745%	$150.3058	$150.31	$150.30	$150.30
Purchase #7	$215.40	9.850%	$236.6169	$236.62	$236.60	$236.60
7 purchase totals =	$1,186.64		$1,272.6272	$1,272.64	$1,272.60	$1,272.50