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	$40.42	12.705%	$45.5554	$45.56	$45.55	$45.60
Purchase #2	$92.51	10.786%	$102.4881	$102.49	$102.50	$102.50
Purchase #3	$14.55	4.864%	$15.2577	$15.26	$15.25	$15.30
Purchase #4	$90.32	12.677%	$101.7699	$101.77	$101.75	$101.80
Purchase #5	$88.89	11.658%	$99.2528	$99.25	$99.25	$99.30
Purchase #6	$176.97	13.839%	$201.4609	$201.46	$201.45	$201.50
Purchase #7	$17.98	13.217%	$20.3564	$20.36	$20.35	$20.40
7 purchase totals =	$521.64		$586.1412	$586.15	$586.10	$586.40