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	$84.96	5.252%	$89.4221	$89.42	$89.40	$89.40
Purchase #2	$126.73	4.817%	$132.8346	$132.83	$132.85	$132.80
Purchase #3	$57.33	13.317%	$64.9646	$64.96	$64.95	$65.00
Purchase #4	$164.99	3.698%	$171.0913	$171.09	$171.10	$171.10
Purchase #5	$10.89	11.247%	$12.1148	$12.11	$12.10	$12.10
Purchase #6	$28.60	11.157%	$31.7909	$31.79	$31.80	$31.80
Purchase #7	$73.75	10.368%	$81.3964	$81.40	$81.40	$81.40
7 purchase totals =	$547.25		$583.6147	$583.60	$583.60	$583.60