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	$153.40	13.366%	$173.9034	$173.90	$173.90	$173.90
Purchase #2	$49.40	6.316%	$52.5201	$52.52	$52.50	$52.50
Purchase #3	$33.67	10.867%	$37.3289	$37.33	$37.35	$37.30
Purchase #4	$148.66	3.173%	$153.377	$153.38	$153.40	$153.40
Purchase #5	$29.54	11.289%	$32.8748	$32.87	$32.85	$32.90
Purchase #6	$13.90	13.507%	$15.7775	$15.78	$15.80	$15.80
Purchase #7	$150.98	9.813%	$165.7957	$165.80	$165.80	$165.80
7 purchase totals =	$579.55		$631.5774	$631.58	$631.60	$631.60