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	$121.28	4.757%	$127.0493	$127.05	$127.05	$127.00
Purchase #2	$50.90	7.701%	$54.8198	$54.82	$54.80	$54.80
Purchase #3	$139.69	11.776%	$156.1399	$156.14	$156.15	$156.10
Purchase #4	$171.78	5.136%	$180.6026	$180.60	$180.60	$180.60
Purchase #5	$56.59	4.416%	$59.089	$59.09	$59.10	$59.10
Purchase #6	$73.83	3.528%	$76.4347	$76.43	$76.45	$76.40
Purchase #7	$28.96	6.420%	$30.8192	$30.82	$30.80	$30.80
7 purchase totals =	$643.03		$684.9545	$684.95	$684.95	$684.80