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	$247.42	13.270%	$280.2526	$280.25	$280.25	$280.30
Purchase #2	$49.55	12.690%	$55.8379	$55.84	$55.85	$55.80
Purchase #3	$11.67	7.497%	$12.5449	$12.54	$12.55	$12.50
Purchase #4	$66.35	10.514%	$73.326	$73.33	$73.35	$73.30
Purchase #5	$73.97	11.699%	$82.6238	$82.62	$82.60	$82.60
Purchase #6	$182.92	4.836%	$191.766	$191.77	$191.75	$191.80
Purchase #7	$178.48	3.849%	$185.3497	$185.35	$185.35	$185.30
7 purchase totals =	$810.36		$881.7009	$881.70	$881.70	$881.60