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	$18.48	8.773%	$20.1013	$20.10	$20.10	$20.10
Purchase #2	$147.99	13.862%	$168.5044	$168.50	$168.50	$168.50
Purchase #3	$18.30	9.788%	$20.0912	$20.09	$20.10	$20.10
Purchase #4	$172.27	5.342%	$181.4727	$181.47	$181.45	$181.50
Purchase #5	$32.91	7.827%	$35.4859	$35.49	$35.50	$35.50
Purchase #6	$199.38	6.330%	$212.0008	$212.00	$212.00	$212.00
Purchase #7	$49.32	6.270%	$52.4124	$52.41	$52.40	$52.40
7 purchase totals =	$638.65		$690.0687	$690.06	$690.05	$690.10