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	$159.50	11.217%	$177.3911	$177.39	$177.40	$177.40
Purchase #2	$62.64	6.857%	$66.9352	$66.94	$66.95	$66.90
Purchase #3	$200.29	7.613%	$215.5381	$215.54	$215.55	$215.50
Purchase #4	$7.29	3.827%	$7.569	$7.57	$7.55	$7.60
Purchase #5	$242.44	3.328%	$250.5084	$250.51	$250.50	$250.50
Purchase #6	$219.47	3.677%	$227.5399	$227.54	$227.55	$227.50
Purchase #7	$38.94	6.491%	$41.4676	$41.47	$41.45	$41.50
7 purchase totals =	$930.57		$986.9493	$986.96	$986.95	$986.90