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	$88.57	13.557%	$100.5774	$100.58	$100.60	$100.60
Purchase #2	$98.76	13.772%	$112.3612	$112.36	$112.35	$112.40
Purchase #3	$54.69	8.784%	$59.494	$59.49	$59.50	$59.50
Purchase #4	$240.38	6.224%	$255.3413	$255.34	$255.35	$255.30
Purchase #5	$108.29	5.711%	$114.4744	$114.47	$114.45	$114.50
Purchase #6	$67.55	10.219%	$74.4529	$74.45	$74.45	$74.50
Purchase #7	$10.94	12.378%	$12.2942	$12.29	$12.30	$12.30
7 purchase totals =	$669.18		$728.9954	$728.98	$729.00	$729.10