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	$124.71	11.707%	$139.3098	$139.31	$139.30	$139.30
Purchase #2	$42.76	8.769%	$46.5096	$46.51	$46.50	$46.50
Purchase #3	$233.73	13.413%	$265.0802	$265.08	$265.10	$265.10
Purchase #4	$62.54	11.300%	$69.607	$69.61	$69.60	$69.60
Purchase #5	$247.99	13.610%	$281.7414	$281.74	$281.75	$281.70
Purchase #6	$95.68	13.721%	$108.8083	$108.81	$108.80	$108.80
Purchase #7	$133.25	4.696%	$139.5074	$139.51	$139.50	$139.50
7 purchase totals =	$940.66		$1,050.5637	$1,050.57	$1,050.55	$1,050.50