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	$12.54	7.612%	$13.4945	$13.49	$13.50	$13.50
Purchase #2	$242.83	11.841%	$271.5835	$271.58	$271.60	$271.60
Purchase #3	$127.84	11.483%	$142.5199	$142.52	$142.50	$142.50
Purchase #4	$68.49	4.674%	$71.6912	$71.69	$71.70	$71.70
Purchase #5	$60.25	3.861%	$62.5763	$62.58	$62.60	$62.60
Purchase #6	$24.33	5.684%	$25.7129	$25.71	$25.70	$25.70
Purchase #7	$163.94	9.856%	$180.0979	$180.10	$180.10	$180.10
7 purchase totals =	$700.22		$767.6762	$767.67	$767.70	$767.70