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	$240.80	9.412%	$263.4641	$263.46	$263.45	$263.50
Purchase #2	$194.78	10.779%	$215.7753	$215.78	$215.80	$215.80
Purchase #3	$212.65	12.527%	$239.2887	$239.29	$239.30	$239.30
Purchase #4	$33.53	6.225%	$35.6172	$35.62	$35.60	$35.60
Purchase #5	$246.55	6.617%	$262.8642	$262.86	$262.85	$262.90
Purchase #6	$169.76	8.655%	$184.4527	$184.45	$184.45	$184.50
Purchase #7	$181.96	4.631%	$190.3866	$190.39	$190.40	$190.40
7 purchase totals =	$1,280.03		$1,391.8488	$1,391.85	$1,391.85	$1,392.00