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	$156.81	7.514%	$168.5927	$168.59	$168.60	$168.60
Purchase #2	$132.79	7.761%	$143.0958	$143.10	$143.10	$143.10
Purchase #3	$185.47	3.834%	$192.5809	$192.58	$192.60	$192.60
Purchase #4	$94.32	6.397%	$100.3537	$100.35	$100.35	$100.40
Purchase #5	$106.54	6.401%	$113.3596	$113.36	$113.35	$113.40
Purchase #6	$209.41	13.663%	$238.0217	$238.02	$238.00	$238.00
Purchase #7	$21.77	11.348%	$24.2405	$24.24	$24.25	$24.20
7 purchase totals =	$907.11		$980.2449	$980.24	$980.25	$980.30