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	$81.40	10.673%	$90.0878	$90.09	$90.10	$90.10
Purchase #2	$248.57	7.862%	$268.1126	$268.11	$268.10	$268.10
Purchase #3	$75.30	3.789%	$78.1531	$78.15	$78.15	$78.20
Purchase #4	$140.59	6.699%	$150.0081	$150.01	$150.00	$150.00
Purchase #5	$190.96	3.613%	$197.8594	$197.86	$197.85	$197.90
Purchase #6	$153.43	12.775%	$173.0307	$173.03	$173.05	$173.00
Purchase #7	$178.77	4.377%	$186.5948	$186.59	$186.60	$186.60
7 purchase totals =	$1,069.02		$1,143.8465	$1,143.84	$1,143.85	$1,143.90