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	$21.33	13.315%	$24.1701	$24.17	$24.15	$24.20
Purchase #2	$96.77	9.114%	$105.5896	$105.59	$105.60	$105.60
Purchase #3	$108.87	7.369%	$116.8926	$116.89	$116.90	$116.90
Purchase #4	$86.78	6.497%	$92.4181	$92.42	$92.40	$92.40
Purchase #5	$29.55	5.833%	$31.2737	$31.27	$31.25	$31.30
Purchase #6	$78.38	13.426%	$88.9033	$88.90	$88.90	$88.90
Purchase #7	$209.80	4.485%	$219.2095	$219.21	$219.20	$219.20
7 purchase totals =	$631.48		$678.4569	$678.45	$678.40	$678.50