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	$134.62	5.640%	$142.2126	$142.21	$142.20	$142.20
Purchase #2	$230.46	10.615%	$254.9233	$254.92	$254.90	$254.90
Purchase #3	$213.51	4.242%	$222.5671	$222.57	$222.55	$222.60
Purchase #4	$22.60	4.738%	$23.6708	$23.67	$23.65	$23.70
Purchase #5	$197.89	3.660%	$205.1328	$205.13	$205.15	$205.10
Purchase #6	$129.45	10.872%	$143.5238	$143.52	$143.50	$143.50
Purchase #7	$150.33	12.320%	$168.8507	$168.85	$168.85	$168.90
7 purchase totals =	$1,078.86		$1,160.8811	$1,160.87	$1,160.80	$1,160.90