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	$115.48	10.395%	$127.4841	$127.48	$127.50	$127.50
Purchase #2	$37.35	13.595%	$42.4277	$42.43	$42.45	$42.40
Purchase #3	$15.79	8.538%	$17.1382	$17.14	$17.15	$17.10
Purchase #4	$64.45	12.169%	$72.2929	$72.29	$72.30	$72.30
Purchase #5	$108.79	11.586%	$121.3944	$121.39	$121.40	$121.40
Purchase #6	$162.33	8.806%	$176.6248	$176.62	$176.60	$176.60
Purchase #7	$93.82	10.381%	$103.5595	$103.56	$103.55	$103.60
7 purchase totals =	$598.01		$660.9216	$660.91	$660.95	$660.90