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	$12.49	9.113%	$13.6282	$13.63	$13.65	$13.60
Purchase #2	$82.78	3.445%	$85.6318	$85.63	$85.65	$85.60
Purchase #3	$246.90	13.113%	$279.276	$279.28	$279.30	$279.30
Purchase #4	$44.28	4.270%	$46.1708	$46.17	$46.15	$46.20
Purchase #5	$26.30	7.188%	$28.1904	$28.19	$28.20	$28.20
Purchase #6	$151.87	8.231%	$164.3704	$164.37	$164.35	$164.40
Purchase #7	$100.36	9.225%	$109.6182	$109.62	$109.60	$109.60
7 purchase totals =	$664.98		$726.8858	$726.89	$726.90	$726.90