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	$170.65	3.658%	$176.8924	$176.89	$176.90	$176.90
Purchase #2	$72.45	13.748%	$82.4104	$82.41	$82.40	$82.40
Purchase #3	$49.68	9.747%	$54.5223	$54.52	$54.50	$54.50
Purchase #4	$203.38	12.296%	$228.3876	$228.39	$228.40	$228.40
Purchase #5	$200.39	7.355%	$215.1287	$215.13	$215.15	$215.10
Purchase #6	$107.40	13.613%	$122.0204	$122.02	$122.00	$122.00
Purchase #7	$144.50	10.212%	$159.2563	$159.26	$159.25	$159.30
7 purchase totals =	$948.45		$1,038.6181	$1,038.62	$1,038.60	$1,038.60