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	$157.45	13.305%	$178.3987	$178.40	$178.40	$178.40
Purchase #2	$225.37	4.164%	$234.7544	$234.75	$234.75	$234.80
Purchase #3	$19.64	3.397%	$20.3072	$20.31	$20.30	$20.30
Purchase #4	$243.97	11.609%	$272.2925	$272.29	$272.30	$272.30
Purchase #5	$62.65	6.300%	$66.597	$66.60	$66.60	$66.60
Purchase #6	$211.75	5.345%	$223.068	$223.07	$223.05	$223.10
Purchase #7	$41.31	5.711%	$43.6692	$43.67	$43.65	$43.70
7 purchase totals =	$962.14		$1,039.0870	$1,039.09	$1,039.05	$1,039.20