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	$27.52	6.458%	$29.2972	$29.30	$29.30	$29.30
Purchase #2	$96.63	3.488%	$100.0005	$100.00	$100.00	$100.00
Purchase #3	$121.29	5.279%	$127.6929	$127.69	$127.70	$127.70
Purchase #4	$57.30	6.500%	$61.0245	$61.02	$61.00	$61.00
Purchase #5	$111.28	10.180%	$122.6083	$122.61	$122.60	$122.60
Purchase #6	$108.36	8.389%	$117.4503	$117.45	$117.45	$117.50
Purchase #7	$97.48	7.139%	$104.4391	$104.44	$104.45	$104.40
7 purchase totals =	$619.86		$662.5128	$662.51	$662.50	$662.50