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	$87.48	3.176%	$90.2584	$90.26	$90.25	$90.30
Purchase #2	$217.27	9.354%	$237.5934	$237.59	$237.60	$237.60
Purchase #3	$148.36	11.433%	$165.322	$165.32	$165.30	$165.30
Purchase #4	$119.39	3.225%	$123.2403	$123.24	$123.25	$123.20
Purchase #5	$169.35	13.182%	$191.6737	$191.67	$191.65	$191.70
Purchase #6	$27.68	5.560%	$29.219	$29.22	$29.20	$29.20
Purchase #7	$34.39	11.796%	$38.4466	$38.45	$38.45	$38.40
7 purchase totals =	$803.92		$875.7534	$875.75	$875.70	$875.70