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	$146.94	13.591%	$166.9106	$166.91	$166.90	$166.90
Purchase #2	$221.85	6.522%	$236.3191	$236.32	$236.30	$236.30
Purchase #3	$137.97	10.592%	$152.5838	$152.58	$152.60	$152.60
Purchase #4	$25.38	8.206%	$27.4627	$27.46	$27.45	$27.50
Purchase #5	$248.54	7.396%	$266.922	$266.92	$266.90	$266.90
Purchase #6	$34.92	3.274%	$36.0633	$36.06	$36.05	$36.10
Purchase #7	$103.64	13.129%	$117.2469	$117.25	$117.25	$117.20
7 purchase totals =	$919.24		$1,003.5084	$1,003.50	$1,003.45	$1,003.50