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	$130.59	13.373%	$148.0538	$148.05	$148.05	$148.10
Purchase #2	$149.77	10.741%	$165.8568	$165.86	$165.85	$165.90
Purchase #3	$65.98	5.464%	$69.5851	$69.59	$69.60	$69.60
Purchase #4	$12.78	5.576%	$13.4926	$13.49	$13.50	$13.50
Purchase #5	$24.45	4.276%	$25.4955	$25.50	$25.50	$25.50
Purchase #6	$80.62	9.278%	$88.0999	$88.10	$88.10	$88.10
Purchase #7	$73.84	9.447%	$80.8157	$80.82	$80.80	$80.80
7 purchase totals =	$538.03		$591.3994	$591.41	$591.40	$591.50