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	$19.85	6.283%	$21.0972	$21.10	$21.10	$21.10
Purchase #2	$177.54	4.679%	$185.8471	$185.85	$185.85	$185.80
Purchase #3	$10.71	10.299%	$11.813	$11.81	$11.80	$11.80
Purchase #4	$33.37	10.344%	$36.8218	$36.82	$36.80	$36.80
Purchase #5	$247.45	7.284%	$265.4743	$265.47	$265.45	$265.50
Purchase #6	$22.43	9.453%	$24.5503	$24.55	$24.55	$24.60
Purchase #7	$117.94	3.123%	$121.6233	$121.62	$121.60	$121.60
7 purchase totals =	$629.29		$667.2270	$667.22	$667.15	$667.20