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	$118.42	7.523%	$127.3287	$127.33	$127.35	$127.30
Purchase #2	$40.39	6.325%	$42.9447	$42.94	$42.95	$42.90
Purchase #3	$88.62	7.871%	$95.5953	$95.60	$95.60	$95.60
Purchase #4	$233.31	11.803%	$260.8476	$260.85	$260.85	$260.80
Purchase #5	$22.33	12.349%	$25.0875	$25.09	$25.10	$25.10
Purchase #6	$16.56	11.518%	$18.4674	$18.47	$18.45	$18.50
Purchase #7	$102.27	3.127%	$105.468	$105.47	$105.45	$105.50
7 purchase totals =	$621.90		$675.7392	$675.75	$675.75	$675.70