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	$37.31	5.784%	$39.468	$39.47	$39.45	$39.50
Purchase #2	$213.66	11.347%	$237.904	$237.90	$237.90	$237.90
Purchase #3	$29.46	8.716%	$32.0277	$32.03	$32.05	$32.00
Purchase #4	$74.63	7.527%	$80.2474	$80.25	$80.25	$80.20
Purchase #5	$89.88	11.249%	$99.9906	$99.99	$100.00	$100.00
Purchase #6	$76.63	11.577%	$85.5015	$85.50	$85.50	$85.50
Purchase #7	$150.59	11.719%	$168.2376	$168.24	$168.25	$168.20
7 purchase totals =	$672.16		$743.3768	$743.38	$743.40	$743.30