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	$155.40	9.652%	$170.3992	$170.40	$170.40	$170.40
Purchase #2	$146.77	5.500%	$154.8424	$154.84	$154.85	$154.80
Purchase #3	$47.33	3.194%	$48.8417	$48.84	$48.85	$48.80
Purchase #4	$52.60	12.757%	$59.3102	$59.31	$59.30	$59.30
Purchase #5	$110.91	11.528%	$123.6957	$123.70	$123.70	$123.70
Purchase #6	$128.52	10.756%	$142.3436	$142.34	$142.35	$142.30
Purchase #7	$196.66	8.395%	$213.1696	$213.17	$213.15	$213.20
7 purchase totals =	$838.19		$912.6024	$912.60	$912.60	$912.50