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	$210.67	12.107%	$236.1758	$236.18	$236.20	$236.20
Purchase #2	$159.29	4.699%	$166.775	$166.78	$166.80	$166.80
Purchase #3	$174.61	13.850%	$198.7935	$198.79	$198.80	$198.80
Purchase #4	$86.79	3.652%	$89.9596	$89.96	$89.95	$90.00
Purchase #5	$151.83	10.447%	$167.6917	$167.69	$167.70	$167.70
Purchase #6	$174.38	10.649%	$192.9497	$192.95	$192.95	$192.90
Purchase #7	$50.78	5.298%	$53.4703	$53.47	$53.45	$53.50
7 purchase totals =	$1,008.35		$1,105.8156	$1,105.82	$1,105.85	$1,105.90