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	$127.29	8.821%	$138.5183	$138.52	$138.50	$138.50
Purchase #2	$50.99	6.386%	$54.2462	$54.25	$54.25	$54.20
Purchase #3	$166.51	9.786%	$182.8047	$182.80	$182.80	$182.80
Purchase #4	$104.26	3.153%	$107.5473	$107.55	$107.55	$107.50
Purchase #5	$35.47	9.321%	$38.7762	$38.78	$38.80	$38.80
Purchase #6	$153.82	3.304%	$158.9022	$158.90	$158.90	$158.90
Purchase #7	$85.68	4.751%	$89.7507	$89.75	$89.75	$89.80
7 purchase totals =	$724.02		$770.5456	$770.55	$770.55	$770.50