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	$155.59	8.765%	$169.2275	$169.23	$169.25	$169.20
Purchase #2	$38.41	9.556%	$42.0805	$42.08	$42.10	$42.10
Purchase #3	$165.61	12.354%	$186.0695	$186.07	$186.05	$186.10
Purchase #4	$247.73	9.521%	$271.3164	$271.32	$271.30	$271.30
Purchase #5	$142.74	5.376%	$150.4137	$150.41	$150.40	$150.40
Purchase #6	$51.88	7.152%	$55.5905	$55.59	$55.60	$55.60
Purchase #7	$38.85	11.643%	$43.3733	$43.37	$43.35	$43.40
7 purchase totals =	$840.81		$918.0714	$918.07	$918.05	$918.10