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	$17.63	3.645%	$18.2726	$18.27	$18.25	$18.30
Purchase #2	$47.42	3.383%	$49.0242	$49.02	$49.00	$49.00
Purchase #3	$239.62	6.476%	$255.1378	$255.14	$255.15	$255.10
Purchase #4	$9.71	6.494%	$10.3406	$10.34	$10.35	$10.30
Purchase #5	$66.51	7.530%	$71.5182	$71.52	$71.50	$71.50
Purchase #6	$12.69	5.415%	$13.3772	$13.38	$13.40	$13.40
Purchase #7	$61.40	9.596%	$67.2919	$67.29	$67.30	$67.30
7 purchase totals =	$454.98		$484.9625	$484.96	$484.95	$484.90