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	$42.73	5.493%	$45.0772	$45.08	$45.10	$45.10
Purchase #2	$168.35	13.105%	$190.4123	$190.41	$190.40	$190.40
Purchase #3	$77.96	5.542%	$82.2805	$82.28	$82.30	$82.30
Purchase #4	$167.68	8.304%	$181.6041	$181.60	$181.60	$181.60
Purchase #5	$11.63	3.848%	$12.0775	$12.08	$12.10	$12.10
Purchase #6	$142.86	10.218%	$157.4574	$157.46	$157.45	$157.50
Purchase #7	$229.66	9.262%	$250.9311	$250.93	$250.95	$250.90
7 purchase totals =	$840.87		$919.8401	$919.84	$919.90	$919.90