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	$137.50	9.146%	$150.0758	$150.08	$150.10	$150.10
Purchase #2	$235.26	4.275%	$245.3174	$245.32	$245.30	$245.30
Purchase #3	$39.92	10.468%	$44.0988	$44.10	$44.10	$44.10
Purchase #4	$171.59	9.622%	$188.1004	$188.10	$188.10	$188.10
Purchase #5	$18.60	4.652%	$19.4653	$19.47	$19.45	$19.50
Purchase #6	$41.98	5.334%	$44.2192	$44.22	$44.20	$44.20
Purchase #7	$111.78	13.686%	$127.0782	$127.08	$127.10	$127.10
7 purchase totals =	$756.63		$818.3551	$818.37	$818.35	$818.40