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	$172.55	3.481%	$178.5565	$178.56	$178.55	$178.60
Purchase #2	$113.36	12.849%	$127.9256	$127.93	$127.95	$127.90
Purchase #3	$69.42	8.339%	$75.2089	$75.21	$75.20	$75.20
Purchase #4	$119.57	5.523%	$126.1739	$126.17	$126.15	$126.20
Purchase #5	$131.48	9.266%	$143.6629	$143.66	$143.65	$143.70
Purchase #6	$70.31	3.223%	$72.5761	$72.58	$72.60	$72.60
Purchase #7	$43.56	4.215%	$45.3961	$45.40	$45.40	$45.40
7 purchase totals =	$720.25		$769.5000	$769.51	$769.50	$769.60