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	$115.53	12.596%	$130.0822	$130.08	$130.10	$130.10
Purchase #2	$24.88	12.565%	$28.0062	$28.01	$28.00	$28.00
Purchase #3	$124.51	12.298%	$139.8222	$139.82	$139.80	$139.80
Purchase #4	$192.38	3.842%	$199.7712	$199.77	$199.75	$199.80
Purchase #5	$223.60	6.668%	$238.5096	$238.51	$238.50	$238.50
Purchase #6	$166.36	7.418%	$178.7006	$178.70	$178.70	$178.70
Purchase #7	$72.83	13.143%	$82.402	$82.40	$82.40	$82.40
7 purchase totals =	$920.09		$997.2940	$997.29	$997.25	$997.30