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	$214.56	12.501%	$241.3821	$241.38	$241.40	$241.40
Purchase #2	$29.80	12.188%	$33.432	$33.43	$33.45	$33.40
Purchase #3	$203.86	8.374%	$220.9312	$220.93	$220.95	$220.90
Purchase #4	$73.79	4.782%	$77.3186	$77.32	$77.30	$77.30
Purchase #5	$107.68	4.767%	$112.8131	$112.81	$112.80	$112.80
Purchase #6	$47.61	13.551%	$54.0616	$54.06	$54.05	$54.10
Purchase #7	$96.26	3.360%	$99.4943	$99.49	$99.50	$99.50
7 purchase totals =	$773.56		$839.4329	$839.42	$839.45	$839.40