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	$14.96	11.218%	$16.6382	$16.64	$16.65	$16.60
Purchase #2	$123.87	5.344%	$130.4896	$130.49	$130.50	$130.50
Purchase #3	$241.59	13.588%	$274.4172	$274.42	$274.40	$274.40
Purchase #4	$41.61	4.522%	$43.4916	$43.49	$43.50	$43.50
Purchase #5	$90.48	9.149%	$98.758	$98.76	$98.75	$98.80
Purchase #6	$70.75	11.452%	$78.8523	$78.85	$78.85	$78.90
Purchase #7	$175.93	13.272%	$199.2794	$199.28	$199.30	$199.30
7 purchase totals =	$759.19		$841.9263	$841.93	$841.95	$842.00