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	$74.59	11.734%	$83.3424	$83.34	$83.35	$83.30
Purchase #2	$168.96	12.596%	$190.2422	$190.24	$190.25	$190.20
Purchase #3	$55.38	12.716%	$62.4221	$62.42	$62.40	$62.40
Purchase #4	$231.63	6.763%	$247.2951	$247.30	$247.30	$247.30
Purchase #5	$136.78	6.481%	$145.6447	$145.64	$145.65	$145.60
Purchase #6	$173.69	6.693%	$185.3151	$185.32	$185.30	$185.30
Purchase #7	$205.60	4.793%	$215.4544	$215.45	$215.45	$215.50
7 purchase totals =	$1,046.63		$1,129.7160	$1,129.71	$1,129.70	$1,129.60