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	$169.60	11.675%	$189.4008	$189.40	$189.40	$189.40
Purchase #2	$105.77	9.549%	$115.87	$115.87	$115.85	$115.90
Purchase #3	$83.44	8.427%	$90.4715	$90.47	$90.45	$90.50
Purchase #4	$161.88	3.218%	$167.0893	$167.09	$167.10	$167.10
Purchase #5	$207.39	7.465%	$222.8717	$222.87	$222.85	$222.90
Purchase #6	$78.57	10.386%	$86.7303	$86.73	$86.75	$86.70
Purchase #7	$12.91	5.109%	$13.5696	$13.57	$13.55	$13.60
7 purchase totals =	$819.56		$886.0032	$886.00	$885.95	$886.10