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	$20.48	3.383%	$21.1728	$21.17	$21.15	$21.20
Purchase #2	$54.71	11.846%	$61.1909	$61.19	$61.20	$61.20
Purchase #3	$162.84	11.684%	$181.8662	$181.87	$181.85	$181.90
Purchase #4	$107.64	11.325%	$119.8302	$119.83	$119.85	$119.80
Purchase #5	$57.77	4.105%	$60.1415	$60.14	$60.15	$60.10
Purchase #6	$44.52	5.228%	$46.8475	$46.85	$46.85	$46.80
Purchase #7	$127.70	6.717%	$136.2776	$136.28	$136.30	$136.30
7 purchase totals =	$575.66		$627.3267	$627.33	$627.35	$627.30