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	$70.55	11.273%	$78.5031	$78.50	$78.50	$78.50
Purchase #2	$49.69	11.581%	$55.4446	$55.44	$55.45	$55.40
Purchase #3	$144.88	10.552%	$160.1677	$160.17	$160.15	$160.20
Purchase #4	$77.88	5.493%	$82.1579	$82.16	$82.15	$82.20
Purchase #5	$164.89	9.177%	$180.022	$180.02	$180.00	$180.00
Purchase #6	$166.41	8.287%	$180.2004	$180.20	$180.20	$180.20
Purchase #7	$11.90	6.338%	$12.6542	$12.65	$12.65	$12.70
7 purchase totals =	$686.20		$749.1499	$749.14	$749.10	$749.20