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	$174.82	9.540%	$191.4978	$191.50	$191.50	$191.50
Purchase #2	$159.91	5.321%	$168.4188	$168.42	$168.40	$168.40
Purchase #3	$168.28	4.587%	$175.999	$176.00	$176.00	$176.00
Purchase #4	$7.29	7.432%	$7.8318	$7.83	$7.85	$7.80
Purchase #5	$162.36	11.756%	$181.447	$181.45	$181.45	$181.40
Purchase #6	$19.72	8.748%	$21.4451	$21.45	$21.45	$21.40
Purchase #7	$155.30	12.363%	$174.4997	$174.50	$174.50	$174.50
7 purchase totals =	$847.68		$921.1392	$921.15	$921.15	$921.00