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	$113.78	8.712%	$123.6925	$123.69	$123.70	$123.70
Purchase #2	$234.87	13.416%	$266.3802	$266.38	$266.40	$266.40
Purchase #3	$173.28	13.286%	$196.302	$196.30	$196.30	$196.30
Purchase #4	$228.99	9.112%	$249.8556	$249.86	$249.85	$249.90
Purchase #5	$63.57	11.418%	$70.8284	$70.83	$70.85	$70.80
Purchase #6	$175.50	7.183%	$188.1062	$188.11	$188.10	$188.10
Purchase #7	$181.59	13.259%	$205.667	$205.67	$205.65	$205.70
7 purchase totals =	$1,171.58		$1,300.8319	$1,300.84	$1,300.85	$1,300.90