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	$91.97	8.833%	$100.0937	$100.09	$100.10	$100.10
Purchase #2	$86.26	4.473%	$90.1184	$90.12	$90.10	$90.10
Purchase #3	$37.50	5.210%	$39.4538	$39.45	$39.45	$39.50
Purchase #4	$98.82	6.768%	$105.5081	$105.51	$105.50	$105.50
Purchase #5	$212.36	4.113%	$221.0944	$221.09	$221.10	$221.10
Purchase #6	$142.75	6.353%	$151.8189	$151.82	$151.80	$151.80
Purchase #7	$190.83	10.316%	$210.516	$210.52	$210.50	$210.50
7 purchase totals =	$860.49		$918.6033	$918.60	$918.55	$918.60