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	$64.90	13.404%	$73.5992	$73.60	$73.60	$73.60
Purchase #2	$136.33	13.563%	$154.8204	$154.82	$154.80	$154.80
Purchase #3	$31.54	12.346%	$35.4339	$35.43	$35.45	$35.40
Purchase #4	$244.28	3.296%	$252.3315	$252.33	$252.35	$252.30
Purchase #5	$78.37	11.331%	$87.2501	$87.25	$87.25	$87.30
Purchase #6	$122.39	4.170%	$127.4937	$127.49	$127.50	$127.50
Purchase #7	$234.82	4.179%	$244.6331	$244.63	$244.65	$244.60
7 purchase totals =	$912.63		$975.5619	$975.55	$975.60	$975.50