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	$160.78	3.569%	$166.5182	$166.52	$166.50	$166.50
Purchase #2	$50.89	9.337%	$55.6416	$55.64	$55.65	$55.60
Purchase #3	$170.93	7.415%	$183.6045	$183.60	$183.60	$183.60
Purchase #4	$35.77	4.320%	$37.3153	$37.32	$37.30	$37.30
Purchase #5	$101.36	13.654%	$115.1997	$115.20	$115.20	$115.20
Purchase #6	$74.30	12.682%	$83.7227	$83.72	$83.70	$83.70
Purchase #7	$176.71	13.622%	$200.7814	$200.78	$200.80	$200.80
7 purchase totals =	$770.74		$842.7834	$842.78	$842.75	$842.70