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	$72.40	8.335%	$78.4345	$78.43	$78.45	$78.40
Purchase #2	$153.46	9.126%	$167.4648	$167.46	$167.45	$167.50
Purchase #3	$87.99	4.330%	$91.8	$91.80	$91.80	$91.80
Purchase #4	$82.58	9.510%	$90.4334	$90.43	$90.45	$90.40
Purchase #5	$81.86	4.163%	$85.2678	$85.27	$85.25	$85.30
Purchase #6	$60.73	11.295%	$67.5895	$67.59	$67.60	$67.60
Purchase #7	$93.87	9.726%	$102.9998	$103.00	$103.00	$103.00
7 purchase totals =	$632.89		$683.9898	$683.98	$684.00	$684.00