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	$169.30	12.393%	$190.2813	$190.28	$190.30	$190.30
Purchase #2	$50.46	8.652%	$54.8258	$54.83	$54.85	$54.80
Purchase #3	$90.60	3.623%	$93.8824	$93.88	$93.90	$93.90
Purchase #4	$100.25	12.307%	$112.5878	$112.59	$112.60	$112.60
Purchase #5	$17.45	5.702%	$18.445	$18.45	$18.45	$18.40
Purchase #6	$191.86	13.536%	$217.8302	$217.83	$217.85	$217.80
Purchase #7	$209.76	11.792%	$234.4949	$234.49	$234.50	$234.50
7 purchase totals =	$829.68		$922.3474	$922.35	$922.45	$922.30