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	$21.33	13.612%	$24.2334	$24.23	$24.25	$24.20
Purchase #2	$73.47	13.603%	$83.4641	$83.46	$83.45	$83.50
Purchase #3	$13.97	11.237%	$15.5398	$15.54	$15.55	$15.50
Purchase #4	$99.75	5.316%	$105.0527	$105.05	$105.05	$105.10
Purchase #5	$173.29	5.239%	$182.3687	$182.37	$182.35	$182.40
Purchase #6	$78.60	13.686%	$89.3572	$89.36	$89.35	$89.40
Purchase #7	$218.76	5.511%	$230.8159	$230.82	$230.80	$230.80
7 purchase totals =	$679.17		$730.8318	$730.83	$730.80	$730.90