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	$250.63	3.551%	$259.5299	$259.53	$259.55	$259.50
Purchase #2	$144.87	8.387%	$157.0202	$157.02	$157.00	$157.00
Purchase #3	$112.32	13.237%	$127.1878	$127.19	$127.20	$127.20
Purchase #4	$96.58	8.533%	$104.8212	$104.82	$104.80	$104.80
Purchase #5	$11.94	6.282%	$12.6901	$12.69	$12.70	$12.70
Purchase #6	$50.90	4.260%	$53.0683	$53.07	$53.05	$53.10
Purchase #7	$77.71	11.836%	$86.9078	$86.91	$86.90	$86.90
7 purchase totals =	$744.95		$801.2253	$801.23	$801.20	$801.20