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	$55.35	3.845%	$57.4782	$57.48	$57.50	$57.50
Purchase #2	$167.51	3.544%	$173.4466	$173.45	$173.45	$173.40
Purchase #3	$64.86	5.329%	$68.3164	$68.32	$68.30	$68.30
Purchase #4	$99.74	11.523%	$111.233	$111.23	$111.25	$111.20
Purchase #5	$118.33	4.645%	$123.8264	$123.83	$123.85	$123.80
Purchase #6	$11.86	13.670%	$13.4813	$13.48	$13.50	$13.50
Purchase #7	$48.38	12.108%	$54.2379	$54.24	$54.25	$54.20
7 purchase totals =	$566.03		$602.0198	$602.03	$602.10	$601.90