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	$51.60	12.497%	$58.0485	$58.05	$58.05	$58.00
Purchase #2	$167.76	10.465%	$185.3161	$185.32	$185.30	$185.30
Purchase #3	$127.50	12.850%	$143.8838	$143.88	$143.90	$143.90
Purchase #4	$169.86	12.245%	$190.6594	$190.66	$190.65	$190.70
Purchase #5	$27.84	13.810%	$31.6847	$31.68	$31.70	$31.70
Purchase #6	$99.44	12.277%	$111.6482	$111.65	$111.65	$111.60
Purchase #7	$117.93	13.251%	$133.5569	$133.56	$133.55	$133.60
7 purchase totals =	$761.93		$854.7976	$854.80	$854.80	$854.80