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	$36.47	11.627%	$40.7104	$40.71	$40.70	$40.70
Purchase #2	$147.57	8.740%	$160.4676	$160.47	$160.45	$160.50
Purchase #3	$11.75	9.187%	$12.8295	$12.83	$12.85	$12.80
Purchase #4	$225.38	12.533%	$253.6269	$253.63	$253.65	$253.60
Purchase #5	$22.45	4.351%	$23.4268	$23.43	$23.45	$23.40
Purchase #6	$92.56	7.459%	$99.4641	$99.46	$99.45	$99.50
Purchase #7	$91.55	3.812%	$95.0399	$95.04	$95.05	$95.00
7 purchase totals =	$627.73		$685.5652	$685.57	$685.60	$685.50