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	$166.95	5.449%	$176.0471	$176.05	$176.05	$176.00
Purchase #2	$38.48	9.228%	$42.0309	$42.03	$42.05	$42.00
Purchase #3	$49.90	12.108%	$55.9419	$55.94	$55.95	$55.90
Purchase #4	$137.43	13.411%	$155.8607	$155.86	$155.85	$155.90
Purchase #5	$199.44	3.597%	$206.6139	$206.61	$206.60	$206.60
Purchase #6	$93.74	8.784%	$101.9741	$101.97	$101.95	$102.00
Purchase #7	$112.43	13.374%	$127.4664	$127.47	$127.45	$127.50
7 purchase totals =	$798.37		$865.9350	$865.93	$865.90	$865.90