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	$40.87	12.110%	$45.8194	$45.82	$45.80	$45.80
Purchase #2	$246.30	13.849%	$280.4101	$280.41	$280.40	$280.40
Purchase #3	$155.37	11.712%	$173.5669	$173.57	$173.55	$173.60
Purchase #4	$141.79	13.748%	$161.2833	$161.28	$161.30	$161.30
Purchase #5	$133.37	12.404%	$149.9132	$149.91	$149.90	$149.90
Purchase #6	$40.49	10.192%	$44.6167	$44.62	$44.60	$44.60
Purchase #7	$174.86	6.267%	$185.8185	$185.82	$185.80	$185.80
7 purchase totals =	$933.05		$1,041.4281	$1,041.43	$1,041.35	$1,041.40