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	$16.27	12.337%	$18.2772	$18.28	$18.30	$18.30
Purchase #2	$198.47	5.443%	$209.2727	$209.27	$209.25	$209.30
Purchase #3	$230.81	10.765%	$255.6567	$255.66	$255.65	$255.70
Purchase #4	$46.91	8.128%	$50.7228	$50.72	$50.70	$50.70
Purchase #5	$228.60	8.295%	$247.5624	$247.56	$247.55	$247.60
Purchase #6	$194.77	5.699%	$205.8699	$205.87	$205.85	$205.90
Purchase #7	$31.69	12.337%	$35.5996	$35.60	$35.60	$35.60
7 purchase totals =	$947.52		$1,022.9613	$1,022.96	$1,022.90	$1,023.10