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	$183.64	8.115%	$198.5424	$198.54	$198.55	$198.50
Purchase #2	$162.58	3.621%	$168.467	$168.47	$168.45	$168.50
Purchase #3	$74.78	7.497%	$80.3863	$80.39	$80.40	$80.40
Purchase #4	$172.59	12.605%	$194.345	$194.35	$194.35	$194.30
Purchase #5	$142.36	6.505%	$151.6205	$151.62	$151.60	$151.60
Purchase #6	$150.46	10.135%	$165.7091	$165.71	$165.70	$165.70
Purchase #7	$103.45	12.258%	$116.1309	$116.13	$116.15	$116.10
7 purchase totals =	$989.86		$1,075.2012	$1,075.21	$1,075.20	$1,075.10