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	$62.91	9.870%	$69.1192	$69.12	$69.10	$69.10
Purchase #2	$33.67	13.249%	$38.1309	$38.13	$38.15	$38.10
Purchase #3	$241.94	13.206%	$273.8906	$273.89	$273.90	$273.90
Purchase #4	$113.83	8.366%	$123.353	$123.35	$123.35	$123.40
Purchase #5	$239.53	13.406%	$271.6414	$271.64	$271.65	$271.60
Purchase #6	$232.98	4.209%	$242.7861	$242.79	$242.80	$242.80
Purchase #7	$54.39	9.694%	$59.6626	$59.66	$59.65	$59.70
7 purchase totals =	$979.25		$1,078.5838	$1,078.58	$1,078.60	$1,078.60