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	$14.96	11.165%	$16.6303	$16.63	$16.65	$16.60
Purchase #2	$63.66	3.535%	$65.9104	$65.91	$65.90	$65.90
Purchase #3	$158.83	9.187%	$173.4217	$173.42	$173.40	$173.40
Purchase #4	$153.89	13.180%	$174.1727	$174.17	$174.15	$174.20
Purchase #5	$81.43	11.250%	$90.5909	$90.59	$90.60	$90.60
Purchase #6	$89.97	10.191%	$99.1388	$99.14	$99.15	$99.10
Purchase #7	$176.65	6.867%	$188.7806	$188.78	$188.80	$188.80
7 purchase totals =	$739.39		$808.6454	$808.64	$808.65	$808.60