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	$170.33	6.698%	$181.7387	$181.74	$181.75	$181.70
Purchase #2	$132.65	7.719%	$142.8893	$142.89	$142.90	$142.90
Purchase #3	$246.52	10.684%	$272.8582	$272.86	$272.85	$272.90
Purchase #4	$40.82	9.689%	$44.775	$44.78	$44.80	$44.80
Purchase #5	$71.60	11.409%	$79.7688	$79.77	$79.75	$79.80
Purchase #6	$166.50	4.453%	$173.9142	$173.91	$173.90	$173.90
Purchase #7	$102.59	9.275%	$112.1052	$112.11	$112.10	$112.10
7 purchase totals =	$931.01		$1,008.0494	$1,008.06	$1,008.05	$1,008.10