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	$60.60	10.200%	$66.7812	$66.78	$66.80	$66.80
Purchase #2	$139.92	5.828%	$148.0745	$148.07	$148.05	$148.10
Purchase #3	$91.48	5.237%	$96.2708	$96.27	$96.25	$96.30
Purchase #4	$221.29	4.641%	$231.5601	$231.56	$231.55	$231.60
Purchase #5	$79.79	12.803%	$90.0055	$90.01	$90.00	$90.00
Purchase #6	$153.37	4.464%	$160.2164	$160.22	$160.20	$160.20
Purchase #7	$82.71	10.650%	$91.5186	$91.52	$91.50	$91.50
7 purchase totals =	$829.16		$884.4271	$884.43	$884.35	$884.50