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	$42.84	6.439%	$45.5985	$45.60	$45.60	$45.60
Purchase #2	$39.41	7.566%	$42.3918	$42.39	$42.40	$42.40
Purchase #3	$190.34	12.493%	$214.1192	$214.12	$214.10	$214.10
Purchase #4	$89.48	13.215%	$101.3048	$101.30	$101.30	$101.30
Purchase #5	$65.28	7.744%	$70.3353	$70.34	$70.35	$70.30
Purchase #6	$12.87	3.258%	$13.2893	$13.29	$13.30	$13.30
Purchase #7	$42.66	12.698%	$48.077	$48.08	$48.10	$48.10
7 purchase totals =	$482.88		$535.1159	$535.12	$535.15	$535.10