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	$114.87	11.203%	$127.7389	$127.74	$127.75	$127.70
Purchase #2	$74.76	4.108%	$77.8311	$77.83	$77.85	$77.80
Purchase #3	$204.77	12.611%	$230.5935	$230.59	$230.60	$230.60
Purchase #4	$82.33	5.322%	$86.7116	$86.71	$86.70	$86.70
Purchase #5	$105.71	3.152%	$109.042	$109.04	$109.05	$109.00
Purchase #6	$74.88	10.444%	$82.7005	$82.70	$82.70	$82.70
Purchase #7	$55.58	12.226%	$62.3752	$62.38	$62.40	$62.40
7 purchase totals =	$712.90		$776.9928	$776.99	$777.05	$776.90