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	$160.92	4.546%	$168.2354	$168.24	$168.25	$168.20
Purchase #2	$87.90	8.436%	$95.3152	$95.32	$95.30	$95.30
Purchase #3	$18.26	12.306%	$20.5071	$20.51	$20.50	$20.50
Purchase #4	$42.65	13.199%	$48.2794	$48.28	$48.30	$48.30
Purchase #5	$30.87	6.364%	$32.8346	$32.83	$32.85	$32.80
Purchase #6	$136.45	4.705%	$142.87	$142.87	$142.85	$142.90
Purchase #7	$224.77	9.651%	$246.4626	$246.46	$246.45	$246.50
7 purchase totals =	$701.82		$754.5043	$754.51	$754.50	$754.50