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	$148.33	4.718%	$155.3282	$155.33	$155.35	$155.30
Purchase #2	$250.93	11.707%	$280.3064	$280.31	$280.30	$280.30
Purchase #3	$72.75	13.831%	$82.8121	$82.81	$82.80	$82.80
Purchase #4	$144.92	13.125%	$163.9408	$163.94	$163.95	$163.90
Purchase #5	$245.69	5.203%	$258.4733	$258.47	$258.45	$258.50
Purchase #6	$161.91	3.689%	$167.8829	$167.88	$167.90	$167.90
Purchase #7	$142.55	6.521%	$151.8457	$151.85	$151.85	$151.80
7 purchase totals =	$1,167.08		$1,260.5894	$1,260.59	$1,260.60	$1,260.50