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	$103.39	5.248%	$108.8159	$108.82	$108.80	$108.80
Purchase #2	$234.27	6.661%	$249.8747	$249.87	$249.85	$249.90
Purchase #3	$59.41	8.750%	$64.6084	$64.61	$64.60	$64.60
Purchase #4	$112.36	3.758%	$116.5825	$116.58	$116.60	$116.60
Purchase #5	$184.69	8.666%	$200.6952	$200.70	$200.70	$200.70
Purchase #6	$239.43	4.742%	$250.7838	$250.78	$250.80	$250.80
Purchase #7	$224.66	13.566%	$255.1374	$255.14	$255.15	$255.10
7 purchase totals =	$1,158.21		$1,246.4979	$1,246.50	$1,246.50	$1,246.50