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	$74.41	8.595%	$80.8055	$80.81	$80.80	$80.80
Purchase #2	$204.40	8.692%	$222.1664	$222.17	$222.15	$222.20
Purchase #3	$131.57	4.224%	$137.1275	$137.13	$137.15	$137.10
Purchase #4	$89.49	13.640%	$101.6964	$101.70	$101.70	$101.70
Purchase #5	$10.69	10.205%	$11.7809	$11.78	$11.80	$11.80
Purchase #6	$73.44	7.183%	$78.7152	$78.72	$78.70	$78.70
Purchase #7	$30.95	5.409%	$32.6241	$32.62	$32.60	$32.60
7 purchase totals =	$614.95		$664.9160	$664.93	$664.90	$664.90