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	$30.31	10.541%	$33.505	$33.51	$33.50	$33.50
Purchase #2	$221.46	3.847%	$229.9796	$229.98	$230.00	$230.00
Purchase #3	$183.46	7.173%	$196.6196	$196.62	$196.60	$196.60
Purchase #4	$123.94	9.601%	$135.8395	$135.84	$135.85	$135.80
Purchase #5	$138.29	12.397%	$155.4338	$155.43	$155.45	$155.40
Purchase #6	$155.27	6.807%	$165.8392	$165.84	$165.85	$165.80
Purchase #7	$142.37	4.550%	$148.8478	$148.85	$148.85	$148.80
7 purchase totals =	$995.10		$1,066.0645	$1,066.07	$1,066.10	$1,065.90