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	$39.97	6.830%	$42.7	$42.70	$42.70	$42.70
Purchase #2	$90.61	13.499%	$102.8414	$102.84	$102.85	$102.80
Purchase #3	$12.80	4.573%	$13.3853	$13.39	$13.40	$13.40
Purchase #4	$107.34	3.579%	$111.1817	$111.18	$111.20	$111.20
Purchase #5	$133.57	9.259%	$145.9372	$145.94	$145.95	$145.90
Purchase #6	$135.62	6.159%	$143.9728	$143.97	$143.95	$144.00
Purchase #7	$124.90	4.535%	$130.5642	$130.56	$130.55	$130.60
7 purchase totals =	$644.81		$690.5826	$690.58	$690.60	$690.60