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	$51.75	11.762%	$57.8368	$57.84	$57.85	$57.80
Purchase #2	$163.78	9.640%	$179.5684	$179.57	$179.55	$179.60
Purchase #3	$118.78	11.152%	$132.0263	$132.03	$132.05	$132.00
Purchase #4	$237.31	12.205%	$266.2737	$266.27	$266.25	$266.30
Purchase #5	$30.86	5.296%	$32.4943	$32.49	$32.50	$32.50
Purchase #6	$61.52	11.296%	$68.4693	$68.47	$68.45	$68.50
Purchase #7	$177.86	4.445%	$185.7659	$185.77	$185.75	$185.80
7 purchase totals =	$841.86		$922.4347	$922.44	$922.40	$922.50