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	$103.88	5.758%	$109.8614	$109.86	$109.85	$109.90
Purchase #2	$158.86	9.543%	$174.02	$174.02	$174.00	$174.00
Purchase #3	$18.77	3.178%	$19.3665	$19.37	$19.35	$19.40
Purchase #4	$149.66	10.663%	$165.6182	$165.62	$165.60	$165.60
Purchase #5	$120.34	5.539%	$127.0056	$127.01	$127.00	$127.00
Purchase #6	$37.40	13.564%	$42.4729	$42.47	$42.45	$42.50
Purchase #7	$16.58	4.746%	$17.3669	$17.37	$17.35	$17.40
7 purchase totals =	$605.49		$655.7115	$655.72	$655.60	$655.80