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	$83.93	7.465%	$90.1954	$90.20	$90.20	$90.20
Purchase #2	$63.77	12.758%	$71.9058	$71.91	$71.90	$71.90
Purchase #3	$49.38	8.110%	$53.3847	$53.38	$53.40	$53.40
Purchase #4	$52.64	3.443%	$54.4524	$54.45	$54.45	$54.50
Purchase #5	$243.37	6.148%	$258.3324	$258.33	$258.35	$258.30
Purchase #6	$106.52	9.501%	$116.6405	$116.64	$116.65	$116.60
Purchase #7	$241.90	7.723%	$260.5819	$260.58	$260.60	$260.60
7 purchase totals =	$841.51		$905.4931	$905.49	$905.55	$905.50