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	$67.89	12.680%	$76.4985	$76.50	$76.50	$76.50
Purchase #2	$126.57	10.174%	$139.4472	$139.45	$139.45	$139.40
Purchase #3	$174.60	9.565%	$191.3005	$191.30	$191.30	$191.30
Purchase #4	$97.77	8.145%	$105.7334	$105.73	$105.75	$105.70
Purchase #5	$179.98	5.457%	$189.8015	$189.80	$189.80	$189.80
Purchase #6	$51.26	5.619%	$54.1403	$54.14	$54.15	$54.10
Purchase #7	$224.38	12.853%	$253.2196	$253.22	$253.20	$253.20
7 purchase totals =	$922.45		$1,010.1410	$1,010.14	$1,010.15	$1,010.00