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	$229.64	12.561%	$258.4851	$258.49	$258.50	$258.50
Purchase #2	$204.82	6.553%	$218.2419	$218.24	$218.25	$218.20
Purchase #3	$95.29	8.390%	$103.2848	$103.28	$103.30	$103.30
Purchase #4	$153.83	13.150%	$174.0586	$174.06	$174.05	$174.10
Purchase #5	$209.57	4.871%	$219.7782	$219.78	$219.80	$219.80
Purchase #6	$122.55	3.667%	$127.0439	$127.04	$127.05	$127.00
Purchase #7	$94.81	10.795%	$105.0447	$105.04	$105.05	$105.00
7 purchase totals =	$1,110.51		$1,205.9372	$1,205.93	$1,206.00	$1,205.90