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	$99.43	4.143%	$103.5494	$103.55	$103.55	$103.50
Purchase #2	$133.62	6.652%	$142.5084	$142.51	$142.50	$142.50
Purchase #3	$74.32	9.867%	$81.6532	$81.65	$81.65	$81.70
Purchase #4	$178.83	6.582%	$190.6006	$190.60	$190.60	$190.60
Purchase #5	$132.55	6.204%	$140.7734	$140.77	$140.75	$140.80
Purchase #6	$95.33	10.616%	$105.4502	$105.45	$105.45	$105.50
Purchase #7	$61.63	13.242%	$69.791	$69.79	$69.80	$69.80
7 purchase totals =	$775.71		$834.3262	$834.32	$834.30	$834.40