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	$30.30	7.619%	$32.6086	$32.61	$32.60	$32.60
Purchase #2	$40.58	12.249%	$45.5506	$45.55	$45.55	$45.60
Purchase #3	$18.38	8.143%	$19.8767	$19.88	$19.90	$19.90
Purchase #4	$105.51	13.506%	$119.7602	$119.76	$119.75	$119.80
Purchase #5	$101.50	4.831%	$106.4035	$106.40	$106.40	$106.40
Purchase #6	$78.33	4.751%	$82.0515	$82.05	$82.05	$82.10
Purchase #7	$155.45	11.861%	$173.8879	$173.89	$173.90	$173.90
7 purchase totals =	$530.05		$580.1390	$580.14	$580.15	$580.30