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	$12.30	8.430%	$13.3369	$13.34	$13.35	$13.30
Purchase #2	$16.75	5.856%	$17.7309	$17.73	$17.75	$17.70
Purchase #3	$135.31	11.210%	$150.4783	$150.48	$150.50	$150.50
Purchase #4	$237.29	7.535%	$255.1698	$255.17	$255.15	$255.20
Purchase #5	$97.56	5.196%	$102.6292	$102.63	$102.65	$102.60
Purchase #6	$121.93	4.394%	$127.2876	$127.29	$127.30	$127.30
Purchase #7	$16.79	10.409%	$18.5377	$18.54	$18.55	$18.50
7 purchase totals =	$637.93		$685.1704	$685.18	$685.25	$685.10