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	$146.59	8.387%	$158.8845	$158.88	$158.90	$158.90
Purchase #2	$165.77	7.753%	$178.6221	$178.62	$178.60	$178.60
Purchase #3	$63.63	5.478%	$67.1157	$67.12	$67.10	$67.10
Purchase #4	$98.48	13.546%	$111.8201	$111.82	$111.80	$111.80
Purchase #5	$232.95	9.488%	$255.0523	$255.05	$255.05	$255.10
Purchase #6	$42.37	8.867%	$46.1269	$46.13	$46.15	$46.10
Purchase #7	$97.31	6.329%	$103.4687	$103.47	$103.45	$103.50
7 purchase totals =	$847.10		$921.0903	$921.09	$921.05	$921.10