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	$37.59	4.364%	$39.2304	$39.23	$39.25	$39.20
Purchase #2	$60.67	4.705%	$63.5245	$63.52	$63.50	$63.50
Purchase #3	$47.36	5.788%	$50.1012	$50.10	$50.10	$50.10
Purchase #4	$145.87	10.209%	$160.7619	$160.76	$160.75	$160.80
Purchase #5	$72.58	5.753%	$76.7555	$76.76	$76.75	$76.80
Purchase #6	$39.44	11.115%	$43.8238	$43.82	$43.80	$43.80
Purchase #7	$144.71	12.250%	$162.437	$162.44	$162.45	$162.40
7 purchase totals =	$548.22		$596.6343	$596.63	$596.60	$596.60