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	$139.25	12.581%	$156.769	$156.77	$156.75	$156.80
Purchase #2	$11.26	10.163%	$12.4044	$12.40	$12.40	$12.40
Purchase #3	$245.84	3.304%	$253.9626	$253.96	$253.95	$254.00
Purchase #4	$102.53	10.808%	$113.6114	$113.61	$113.60	$113.60
Purchase #5	$52.60	13.293%	$59.5921	$59.59	$59.60	$59.60
Purchase #6	$174.86	10.172%	$192.6468	$192.65	$192.65	$192.60
Purchase #7	$181.57	4.212%	$189.2177	$189.22	$189.20	$189.20
7 purchase totals =	$907.91		$978.2040	$978.20	$978.15	$978.20