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	$121.48	10.656%	$134.4249	$134.42	$134.40	$134.40
Purchase #2	$212.32	5.766%	$224.5624	$224.56	$224.55	$224.60
Purchase #3	$242.98	4.790%	$254.6187	$254.62	$254.60	$254.60
Purchase #4	$15.69	9.504%	$17.1812	$17.18	$17.20	$17.20
Purchase #5	$249.86	9.456%	$273.4868	$273.49	$273.50	$273.50
Purchase #6	$134.47	5.690%	$142.1213	$142.12	$142.10	$142.10
Purchase #7	$107.59	3.793%	$111.6709	$111.67	$111.65	$111.70
7 purchase totals =	$1,084.39		$1,158.0662	$1,158.06	$1,158.00	$1,158.10