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	$131.25	10.171%	$144.5994	$144.60	$144.60	$144.60
Purchase #2	$103.59	5.869%	$109.6697	$109.67	$109.65	$109.70
Purchase #3	$218.85	13.843%	$249.1454	$249.15	$249.15	$249.10
Purchase #4	$117.53	11.845%	$131.4514	$131.45	$131.45	$131.50
Purchase #5	$95.77	13.202%	$108.4136	$108.41	$108.40	$108.40
Purchase #6	$31.40	13.811%	$35.7367	$35.74	$35.75	$35.70
Purchase #7	$59.58	11.208%	$66.2577	$66.26	$66.25	$66.30
7 purchase totals =	$757.97		$845.2739	$845.28	$845.25	$845.30