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	$247.94	9.106%	$270.5174	$270.52	$270.50	$270.50
Purchase #2	$33.85	6.745%	$36.1332	$36.13	$36.15	$36.10
Purchase #3	$186.77	4.681%	$195.5127	$195.51	$195.50	$195.50
Purchase #4	$103.32	13.549%	$117.3188	$117.32	$117.30	$117.30
Purchase #5	$86.45	11.637%	$96.5102	$96.51	$96.50	$96.50
Purchase #6	$189.57	13.396%	$214.9648	$214.96	$214.95	$215.00
Purchase #7	$233.50	3.483%	$241.6328	$241.63	$241.65	$241.60
7 purchase totals =	$1,081.40		$1,172.5899	$1,172.58	$1,172.55	$1,172.50