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	$26.97	9.778%	$29.6071	$29.61	$29.60	$29.60
Purchase #2	$14.40	6.596%	$15.3498	$15.35	$15.35	$15.30
Purchase #3	$94.36	5.847%	$99.8772	$99.88	$99.90	$99.90
Purchase #4	$46.91	3.373%	$48.4923	$48.49	$48.50	$48.50
Purchase #5	$127.93	11.293%	$142.3771	$142.38	$142.40	$142.40
Purchase #6	$78.65	12.646%	$88.5961	$88.60	$88.60	$88.60
Purchase #7	$118.82	5.640%	$125.5214	$125.52	$125.50	$125.50
7 purchase totals =	$508.04		$549.8210	$549.83	$549.85	$549.80