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	$65.83	8.210%	$71.2346	$71.23	$71.25	$71.20
Purchase #2	$138.98	3.535%	$143.8929	$143.89	$143.90	$143.90
Purchase #3	$95.88	9.495%	$104.9838	$104.98	$105.00	$105.00
Purchase #4	$159.62	13.159%	$180.6244	$180.62	$180.60	$180.60
Purchase #5	$175.81	11.848%	$196.64	$196.64	$196.65	$196.60
Purchase #6	$32.90	13.295%	$37.2741	$37.27	$37.25	$37.30
Purchase #7	$77.44	13.578%	$87.9548	$87.95	$87.95	$88.00
7 purchase totals =	$746.46		$822.6046	$822.58	$822.60	$822.60