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	$67.82	9.722%	$74.4135	$74.41	$74.40	$74.40
Purchase #2	$92.72	10.197%	$102.1747	$102.17	$102.15	$102.20
Purchase #3	$54.71	5.114%	$57.5079	$57.51	$57.50	$57.50
Purchase #4	$138.73	10.732%	$153.6185	$153.62	$153.60	$153.60
Purchase #5	$146.52	6.193%	$155.594	$155.59	$155.60	$155.60
Purchase #6	$13.90	4.726%	$14.5569	$14.56	$14.55	$14.60
Purchase #7	$106.50	5.260%	$112.1019	$112.10	$112.10	$112.10
7 purchase totals =	$620.90		$669.9674	$669.96	$669.90	$670.00