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	$26.52	10.686%	$29.3539	$29.35	$29.35	$29.40
Purchase #2	$123.47	6.383%	$131.3511	$131.35	$131.35	$131.40
Purchase #3	$86.84	12.595%	$97.7775	$97.78	$97.80	$97.80
Purchase #4	$139.70	13.848%	$159.0457	$159.05	$159.05	$159.00
Purchase #5	$169.79	9.186%	$185.3869	$185.39	$185.40	$185.40
Purchase #6	$38.89	8.641%	$42.2505	$42.25	$42.25	$42.30
Purchase #7	$48.27	10.769%	$53.4682	$53.47	$53.45	$53.50
7 purchase totals =	$633.48		$698.6338	$698.64	$698.65	$698.80