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	$221.88	7.331%	$238.146	$238.15	$238.15	$238.10
Purchase #2	$49.32	10.816%	$54.6545	$54.65	$54.65	$54.70
Purchase #3	$109.59	6.409%	$116.6136	$116.61	$116.60	$116.60
Purchase #4	$115.41	13.480%	$130.9673	$130.97	$130.95	$131.00
Purchase #5	$111.70	6.745%	$119.2342	$119.23	$119.25	$119.20
Purchase #6	$248.56	8.343%	$269.2974	$269.30	$269.30	$269.30
Purchase #7	$26.58	3.376%	$27.4773	$27.48	$27.50	$27.50
7 purchase totals =	$883.04		$956.3903	$956.39	$956.40	$956.40