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	$18.43	7.435%	$19.8003	$19.80	$19.80	$19.80
Purchase #2	$225.63	10.425%	$249.1519	$249.15	$249.15	$249.20
Purchase #3	$143.68	5.729%	$151.9114	$151.91	$151.90	$151.90
Purchase #4	$141.28	4.828%	$148.101	$148.10	$148.10	$148.10
Purchase #5	$66.57	6.661%	$71.0042	$71.00	$71.00	$71.00
Purchase #6	$167.91	6.278%	$178.4514	$178.45	$178.45	$178.50
Purchase #7	$124.36	13.711%	$141.411	$141.41	$141.40	$141.40
7 purchase totals =	$887.86		$959.8312	$959.82	$959.80	$959.90