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	$17.57	13.517%	$19.9449	$19.94	$19.95	$19.90
Purchase #2	$217.26	6.129%	$230.5759	$230.58	$230.60	$230.60
Purchase #3	$49.71	6.766%	$53.0734	$53.07	$53.05	$53.10
Purchase #4	$9.55	10.325%	$10.536	$10.54	$10.55	$10.50
Purchase #5	$88.61	12.421%	$99.6162	$99.62	$99.60	$99.60
Purchase #6	$194.52	11.525%	$216.9384	$216.94	$216.95	$216.90
Purchase #7	$215.50	10.587%	$238.315	$238.32	$238.30	$238.30
7 purchase totals =	$792.72		$868.9998	$869.01	$869.00	$868.90