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	$126.49	12.736%	$142.5998	$142.60	$142.60	$142.60
Purchase #2	$117.61	5.275%	$123.8139	$123.81	$123.80	$123.80
Purchase #3	$111.36	3.465%	$115.2186	$115.22	$115.20	$115.20
Purchase #4	$14.69	6.479%	$15.6418	$15.64	$15.65	$15.60
Purchase #5	$11.64	11.148%	$12.9376	$12.94	$12.95	$12.90
Purchase #6	$35.51	9.344%	$38.8281	$38.83	$38.85	$38.80
Purchase #7	$138.64	10.150%	$152.712	$152.71	$152.70	$152.70
7 purchase totals =	$555.94		$601.7518	$601.75	$601.75	$601.60