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	$28.58	3.663%	$29.6269	$29.63	$29.65	$29.60
Purchase #2	$224.76	13.553%	$255.2217	$255.22	$255.20	$255.20
Purchase #3	$101.77	9.793%	$111.7363	$111.74	$111.75	$111.70
Purchase #4	$95.60	3.782%	$99.2156	$99.22	$99.20	$99.20
Purchase #5	$203.59	11.710%	$227.4304	$227.43	$227.45	$227.40
Purchase #6	$193.94	7.496%	$208.4777	$208.48	$208.50	$208.50
Purchase #7	$50.85	3.614%	$52.6877	$52.69	$52.70	$52.70
7 purchase totals =	$899.09		$984.3963	$984.41	$984.45	$984.30