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	$29.49	4.395%	$30.7861	$30.79	$30.80	$30.80
Purchase #2	$36.58	9.534%	$40.0675	$40.07	$40.05	$40.10
Purchase #3	$43.71	3.795%	$45.3688	$45.37	$45.35	$45.40
Purchase #4	$91.86	12.393%	$103.2442	$103.24	$103.25	$103.20
Purchase #5	$65.92	9.206%	$71.9886	$71.99	$72.00	$72.00
Purchase #6	$241.60	5.844%	$255.7191	$255.72	$255.70	$255.70
Purchase #7	$97.61	4.115%	$101.6267	$101.63	$101.65	$101.60
7 purchase totals =	$606.77		$648.8010	$648.81	$648.80	$648.80