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	$11.29	9.275%	$12.3371	$12.34	$12.35	$12.30
Purchase #2	$226.56	4.809%	$237.4553	$237.46	$237.45	$237.50
Purchase #3	$231.36	4.272%	$241.2437	$241.24	$241.25	$241.20
Purchase #4	$141.81	13.676%	$161.2039	$161.20	$161.20	$161.20
Purchase #5	$52.89	12.135%	$59.3082	$59.31	$59.30	$59.30
Purchase #6	$158.42	5.669%	$167.4008	$167.40	$167.40	$167.40
Purchase #7	$103.88	12.145%	$116.4962	$116.50	$116.50	$116.50
7 purchase totals =	$926.21		$995.4452	$995.45	$995.45	$995.40