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	$85.81	4.769%	$89.9023	$89.90	$89.90	$89.90
Purchase #2	$154.28	8.335%	$167.1392	$167.14	$167.15	$167.10
Purchase #3	$73.52	10.779%	$81.4447	$81.44	$81.45	$81.40
Purchase #4	$107.96	8.332%	$116.9552	$116.96	$116.95	$117.00
Purchase #5	$85.27	5.683%	$90.1159	$90.12	$90.10	$90.10
Purchase #6	$70.60	6.354%	$75.0859	$75.09	$75.10	$75.10
Purchase #7	$178.31	6.650%	$190.1676	$190.17	$190.15	$190.20
7 purchase totals =	$755.75		$810.8108	$810.82	$810.80	$810.80