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	$78.75	4.252%	$82.0985	$82.10	$82.10	$82.10
Purchase #2	$40.81	9.288%	$44.6004	$44.60	$44.60	$44.60
Purchase #3	$65.56	13.103%	$74.1503	$74.15	$74.15	$74.20
Purchase #4	$82.29	10.680%	$91.0786	$91.08	$91.10	$91.10
Purchase #5	$53.43	10.460%	$59.0188	$59.02	$59.00	$59.00
Purchase #6	$193.70	5.558%	$204.4658	$204.47	$204.45	$204.50
Purchase #7	$180.88	12.398%	$203.3055	$203.31	$203.30	$203.30
7 purchase totals =	$695.42		$758.7179	$758.73	$758.70	$758.80