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	$28.85	9.460%	$31.5792	$31.58	$31.60	$31.60
Purchase #2	$249.56	5.244%	$262.6469	$262.65	$262.65	$262.60
Purchase #3	$162.96	9.541%	$178.508	$178.51	$178.50	$178.50
Purchase #4	$103.69	7.323%	$111.2832	$111.28	$111.30	$111.30
Purchase #5	$19.75	4.730%	$20.6842	$20.68	$20.70	$20.70
Purchase #6	$20.89	13.515%	$23.7133	$23.71	$23.70	$23.70
Purchase #7	$210.26	13.418%	$238.4727	$238.47	$238.45	$238.50
7 purchase totals =	$795.96		$866.8875	$866.88	$866.90	$866.90