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	$159.60	6.613%	$170.1543	$170.15	$170.15	$170.20
Purchase #2	$130.39	10.851%	$144.5386	$144.54	$144.55	$144.50
Purchase #3	$94.40	7.811%	$101.7736	$101.77	$101.75	$101.80
Purchase #4	$40.85	3.561%	$42.3047	$42.30	$42.30	$42.30
Purchase #5	$97.81	11.598%	$109.154	$109.15	$109.15	$109.20
Purchase #6	$101.89	13.408%	$115.5514	$115.55	$115.55	$115.60
Purchase #7	$36.85	3.325%	$38.0753	$38.08	$38.10	$38.10
7 purchase totals =	$661.79		$721.5519	$721.54	$721.55	$721.70