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	$175.31	12.132%	$196.5786	$196.58	$196.60	$196.60
Purchase #2	$205.81	12.787%	$232.1269	$232.13	$232.15	$232.10
Purchase #3	$131.94	10.556%	$145.8676	$145.87	$145.85	$145.90
Purchase #4	$39.70	11.840%	$44.4005	$44.40	$44.40	$44.40
Purchase #5	$73.41	5.508%	$77.4534	$77.45	$77.45	$77.50
Purchase #6	$83.87	8.823%	$91.2699	$91.27	$91.25	$91.30
Purchase #7	$40.28	13.495%	$45.7158	$45.72	$45.70	$45.70
7 purchase totals =	$750.32		$833.4127	$833.42	$833.40	$833.50