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	$40.40	4.664%	$42.2843	$42.28	$42.30	$42.30
Purchase #2	$173.63	12.727%	$195.7279	$195.73	$195.75	$195.70
Purchase #3	$81.83	9.510%	$89.612	$89.61	$89.60	$89.60
Purchase #4	$201.69	8.690%	$219.2169	$219.22	$219.20	$219.20
Purchase #5	$167.28	3.522%	$173.1716	$173.17	$173.15	$173.20
Purchase #6	$192.83	9.426%	$211.0062	$211.01	$211.00	$211.00
Purchase #7	$204.60	3.369%	$211.493	$211.49	$211.50	$211.50
7 purchase totals =	$1,062.26		$1,142.5119	$1,142.51	$1,142.50	$1,142.50