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	$144.41	9.818%	$158.5882	$158.59	$158.60	$158.60
Purchase #2	$157.60	13.650%	$179.1124	$179.11	$179.10	$179.10
Purchase #3	$21.31	5.260%	$22.4309	$22.43	$22.45	$22.40
Purchase #4	$24.28	12.651%	$27.3517	$27.35	$27.35	$27.40
Purchase #5	$122.90	13.381%	$139.3452	$139.35	$139.35	$139.30
Purchase #6	$244.83	4.323%	$255.414	$255.41	$255.40	$255.40
Purchase #7	$119.83	8.500%	$130.0156	$130.02	$130.00	$130.00
7 purchase totals =	$835.16		$912.2580	$912.26	$912.25	$912.20