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	$29.67	7.540%	$31.9071	$31.91	$31.90	$31.90
Purchase #2	$144.72	10.320%	$159.6551	$159.66	$159.65	$159.70
Purchase #3	$200.59	13.406%	$227.4811	$227.48	$227.50	$227.50
Purchase #4	$241.48	11.176%	$268.4678	$268.47	$268.45	$268.50
Purchase #5	$237.35	6.631%	$253.0887	$253.09	$253.10	$253.10
Purchase #6	$234.40	9.217%	$256.0046	$256.00	$256.00	$256.00
Purchase #7	$122.63	3.827%	$127.3231	$127.32	$127.30	$127.30
7 purchase totals =	$1,210.84		$1,323.9275	$1,323.93	$1,323.90	$1,324.00