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	$64.34	13.850%	$73.2511	$73.25	$73.25	$73.30
Purchase #2	$53.85	6.542%	$57.3729	$57.37	$57.35	$57.40
Purchase #3	$158.70	8.722%	$172.5418	$172.54	$172.55	$172.50
Purchase #4	$72.57	11.802%	$81.1347	$81.13	$81.15	$81.10
Purchase #5	$11.29	12.806%	$12.7358	$12.74	$12.75	$12.70
Purchase #6	$36.45	12.149%	$40.8783	$40.88	$40.90	$40.90
Purchase #7	$165.30	11.443%	$184.2153	$184.22	$184.20	$184.20
7 purchase totals =	$562.50		$622.1299	$622.13	$622.15	$622.10