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	$138.51	12.248%	$155.4747	$155.47	$155.45	$155.50
Purchase #2	$6.67	6.470%	$7.1015	$7.10	$7.10	$7.10
Purchase #3	$69.46	13.483%	$78.8253	$78.83	$78.85	$78.80
Purchase #4	$43.85	12.237%	$49.2159	$49.22	$49.20	$49.20
Purchase #5	$164.79	12.599%	$185.5519	$185.55	$185.55	$185.60
Purchase #6	$20.45	3.246%	$21.1138	$21.11	$21.10	$21.10
Purchase #7	$152.85	12.745%	$172.3307	$172.33	$172.35	$172.30
7 purchase totals =	$596.58		$669.6138	$669.61	$669.60	$669.60