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	$19.51	4.447%	$20.3776	$20.38	$20.40	$20.40
Purchase #2	$66.53	9.372%	$72.7652	$72.77	$72.75	$72.80
Purchase #3	$18.62	13.870%	$21.2026	$21.20	$21.20	$21.20
Purchase #4	$172.29	3.390%	$178.1306	$178.13	$178.15	$178.10
Purchase #5	$151.95	11.123%	$168.8514	$168.85	$168.85	$168.90
Purchase #6	$41.50	4.745%	$43.4692	$43.47	$43.45	$43.50
Purchase #7	$51.88	8.296%	$56.184	$56.18	$56.20	$56.20
7 purchase totals =	$522.28		$560.9806	$560.98	$561.00	$561.10