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	$92.83	8.258%	$100.4959	$100.50	$100.50	$100.50
Purchase #2	$105.81	9.445%	$115.8038	$115.80	$115.80	$115.80
Purchase #3	$109.81	3.138%	$113.2558	$113.26	$113.25	$113.30
Purchase #4	$20.75	3.134%	$21.4003	$21.40	$21.40	$21.40
Purchase #5	$112.65	3.190%	$116.2435	$116.24	$116.25	$116.20
Purchase #6	$137.45	13.541%	$156.0621	$156.06	$156.05	$156.10
Purchase #7	$235.83	11.221%	$262.2925	$262.29	$262.30	$262.30
7 purchase totals =	$815.13		$885.5539	$885.55	$885.55	$885.60