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	$176.90	9.358%	$193.4543	$193.45	$193.45	$193.50
Purchase #2	$142.75	3.787%	$148.1559	$148.16	$148.15	$148.20
Purchase #3	$117.57	12.521%	$132.2909	$132.29	$132.30	$132.30
Purchase #4	$126.82	10.678%	$140.3618	$140.36	$140.35	$140.40
Purchase #5	$96.93	5.104%	$101.8773	$101.88	$101.90	$101.90
Purchase #6	$43.38	7.455%	$46.614	$46.61	$46.60	$46.60
Purchase #7	$75.96	3.857%	$78.8898	$78.89	$78.90	$78.90
7 purchase totals =	$780.31		$841.6440	$841.64	$841.65	$841.80