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	$82.86	3.181%	$85.4958	$85.50	$85.50	$85.50
Purchase #2	$205.37	7.502%	$220.7769	$220.78	$220.80	$220.80
Purchase #3	$148.37	5.722%	$156.8597	$156.86	$156.85	$156.90
Purchase #4	$154.35	11.453%	$172.0277	$172.03	$172.05	$172.00
Purchase #5	$22.79	3.194%	$23.5179	$23.52	$23.50	$23.50
Purchase #6	$133.40	9.834%	$146.5186	$146.52	$146.50	$146.50
Purchase #7	$139.50	8.412%	$151.2347	$151.23	$151.25	$151.20
7 purchase totals =	$886.64		$956.4313	$956.44	$956.45	$956.40