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	$14.37	12.688%	$16.1933	$16.19	$16.20	$16.20
Purchase #2	$55.93	6.269%	$59.4363	$59.44	$59.45	$59.40
Purchase #3	$158.84	8.626%	$172.5415	$172.54	$172.55	$172.50
Purchase #4	$178.87	7.551%	$192.3765	$192.38	$192.40	$192.40
Purchase #5	$188.35	4.528%	$196.8785	$196.88	$196.90	$196.90
Purchase #6	$230.26	4.834%	$241.3908	$241.39	$241.40	$241.40
Purchase #7	$10.41	9.162%	$11.3638	$11.36	$11.35	$11.40
7 purchase totals =	$837.03		$890.1807	$890.18	$890.25	$890.20