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	$102.69	13.249%	$116.2954	$116.30	$116.30	$116.30
Purchase #2	$106.60	5.111%	$112.0483	$112.05	$112.05	$112.00
Purchase #3	$160.48	7.506%	$172.5256	$172.53	$172.55	$172.50
Purchase #4	$39.86	13.439%	$45.2168	$45.22	$45.20	$45.20
Purchase #5	$95.32	8.512%	$103.4336	$103.43	$103.45	$103.40
Purchase #6	$200.81	11.296%	$223.4935	$223.49	$223.50	$223.50
Purchase #7	$44.63	9.767%	$48.989	$48.99	$49.00	$49.00
7 purchase totals =	$750.39		$822.0022	$822.01	$822.05	$821.90