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	$28.92	11.147%	$32.1437	$32.14	$32.15	$32.10
Purchase #2	$111.95	10.438%	$123.6353	$123.64	$123.65	$123.60
Purchase #3	$95.96	13.201%	$108.6277	$108.63	$108.65	$108.60
Purchase #4	$178.93	12.255%	$200.8579	$200.86	$200.85	$200.90
Purchase #5	$27.27	8.560%	$29.6043	$29.60	$29.60	$29.60
Purchase #6	$215.91	10.614%	$238.8267	$238.83	$238.85	$238.80
Purchase #7	$218.39	8.154%	$236.1975	$236.20	$236.20	$236.20
7 purchase totals =	$877.33		$969.8931	$969.90	$969.95	$969.80