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	$26.99	3.857%	$28.031	$28.03	$28.05	$28.00
Purchase #2	$232.32	11.203%	$258.3468	$258.35	$258.35	$258.30
Purchase #3	$97.86	13.766%	$111.3314	$111.33	$111.35	$111.30
Purchase #4	$184.72	7.504%	$198.5814	$198.58	$198.60	$198.60
Purchase #5	$199.88	10.839%	$221.545	$221.55	$221.55	$221.50
Purchase #6	$56.66	10.107%	$62.3866	$62.39	$62.40	$62.40
Purchase #7	$87.37	12.822%	$98.5726	$98.57	$98.55	$98.60
7 purchase totals =	$885.80		$978.7948	$978.80	$978.85	$978.70