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	$46.71	13.692%	$53.1055	$53.11	$53.10	$53.10
Purchase #2	$133.41	12.624%	$150.2517	$150.25	$150.25	$150.30
Purchase #3	$75.42	4.333%	$78.6879	$78.69	$78.70	$78.70
Purchase #4	$120.53	6.500%	$128.3645	$128.36	$128.35	$128.40
Purchase #5	$62.80	4.179%	$65.4244	$65.42	$65.40	$65.40
Purchase #6	$235.67	8.295%	$255.2188	$255.22	$255.20	$255.20
Purchase #7	$242.63	5.339%	$255.584	$255.58	$255.60	$255.60
7 purchase totals =	$917.17		$986.6368	$986.63	$986.60	$986.70