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	$74.38	7.328%	$79.8306	$79.83	$79.85	$79.80
Purchase #2	$35.42	5.760%	$37.4602	$37.46	$37.45	$37.50
Purchase #3	$87.90	11.560%	$98.0612	$98.06	$98.05	$98.10
Purchase #4	$104.92	10.798%	$116.2493	$116.25	$116.25	$116.20
Purchase #5	$49.67	5.163%	$52.2345	$52.23	$52.25	$52.20
Purchase #6	$155.39	7.131%	$166.4709	$166.47	$166.45	$166.50
Purchase #7	$123.81	3.466%	$128.1013	$128.10	$128.10	$128.10
7 purchase totals =	$631.49		$678.4080	$678.40	$678.40	$678.40