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	$15.86	4.698%	$16.6051	$16.61	$16.60	$16.60
Purchase #2	$75.41	10.194%	$83.0973	$83.10	$83.10	$83.10
Purchase #3	$116.32	9.810%	$127.731	$127.73	$127.75	$127.70
Purchase #4	$237.51	7.265%	$254.7651	$254.77	$254.75	$254.80
Purchase #5	$62.89	7.498%	$67.6055	$67.61	$67.60	$67.60
Purchase #6	$231.47	13.848%	$263.524	$263.52	$263.50	$263.50
Purchase #7	$161.83	9.717%	$177.555	$177.56	$177.55	$177.60
7 purchase totals =	$901.29		$990.8830	$990.90	$990.85	$990.90