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	$233.82	6.743%	$249.5865	$249.59	$249.60	$249.60
Purchase #2	$138.85	9.552%	$152.113	$152.11	$152.10	$152.10
Purchase #3	$55.54	10.330%	$61.2773	$61.28	$61.30	$61.30
Purchase #4	$170.98	3.229%	$176.5009	$176.50	$176.50	$176.50
Purchase #5	$146.52	5.114%	$154.013	$154.01	$154.00	$154.00
Purchase #6	$54.56	12.716%	$61.4978	$61.50	$61.50	$61.50
Purchase #7	$106.40	5.508%	$112.2605	$112.26	$112.25	$112.30
7 purchase totals =	$906.67		$967.2490	$967.25	$967.25	$967.30