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	$26.58	5.205%	$27.9635	$27.96	$27.95	$28.00
Purchase #2	$134.70	7.480%	$144.7756	$144.78	$144.80	$144.80
Purchase #3	$75.83	7.450%	$81.4793	$81.48	$81.50	$81.50
Purchase #4	$39.28	3.668%	$40.7208	$40.72	$40.70	$40.70
Purchase #5	$173.88	9.629%	$190.6229	$190.62	$190.60	$190.60
Purchase #6	$60.26	13.766%	$68.5554	$68.56	$68.55	$68.60
Purchase #7	$69.50	13.317%	$78.7553	$78.76	$78.75	$78.80
7 purchase totals =	$580.03		$632.8728	$632.88	$632.85	$633.00