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	$20.67	10.103%	$22.7583	$22.76	$22.75	$22.80
Purchase #2	$110.35	11.595%	$123.1451	$123.15	$123.15	$123.10
Purchase #3	$132.66	7.721%	$142.9027	$142.90	$142.90	$142.90
Purchase #4	$165.63	11.793%	$185.1627	$185.16	$185.15	$185.20
Purchase #5	$234.41	12.482%	$263.6691	$263.67	$263.65	$263.70
Purchase #6	$145.27	12.446%	$163.3503	$163.35	$163.35	$163.40
Purchase #7	$230.44	8.455%	$249.9237	$249.92	$249.90	$249.90
7 purchase totals =	$1,039.43		$1,150.9119	$1,150.91	$1,150.85	$1,151.00