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	$149.71	7.264%	$160.5849	$160.58	$160.60	$160.60
Purchase #2	$41.76	11.451%	$46.5419	$46.54	$46.55	$46.50
Purchase #3	$46.90	3.304%	$48.4496	$48.45	$48.45	$48.40
Purchase #4	$35.29	13.712%	$40.129	$40.13	$40.15	$40.10
Purchase #5	$84.41	6.739%	$90.0984	$90.10	$90.10	$90.10
Purchase #6	$48.92	3.222%	$50.4962	$50.50	$50.50	$50.50
Purchase #7	$100.84	9.722%	$110.6437	$110.64	$110.65	$110.60
7 purchase totals =	$507.83		$546.9437	$546.94	$547.00	$546.80