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	$87.89	12.214%	$98.6249	$98.62	$98.60	$98.60
Purchase #2	$238.87	6.661%	$254.7811	$254.78	$254.80	$254.80
Purchase #3	$49.99	11.628%	$55.8028	$55.80	$55.80	$55.80
Purchase #4	$77.30	13.777%	$87.9496	$87.95	$87.95	$87.90
Purchase #5	$14.67	3.405%	$15.1695	$15.17	$15.15	$15.20
Purchase #6	$173.52	4.369%	$181.1011	$181.10	$181.10	$181.10
Purchase #7	$82.32	10.364%	$90.8516	$90.85	$90.85	$90.90
7 purchase totals =	$724.56		$784.2806	$784.27	$784.25	$784.30