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	$107.80	11.862%	$120.5872	$120.59	$120.60	$120.60
Purchase #2	$148.67	6.690%	$158.616	$158.62	$158.60	$158.60
Purchase #3	$173.92	10.629%	$192.406	$192.41	$192.40	$192.40
Purchase #4	$99.50	9.599%	$109.051	$109.05	$109.05	$109.10
Purchase #5	$219.88	9.579%	$240.9423	$240.94	$240.95	$240.90
Purchase #6	$13.61	8.709%	$14.7953	$14.80	$14.80	$14.80
Purchase #7	$40.72	10.737%	$45.0921	$45.09	$45.10	$45.10
7 purchase totals =	$804.10		$881.4899	$881.50	$881.50	$881.50