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	$245.43	8.712%	$266.8119	$266.81	$266.80	$266.80
Purchase #2	$50.25	11.141%	$55.8484	$55.85	$55.85	$55.80
Purchase #3	$138.81	5.590%	$146.5695	$146.57	$146.55	$146.60
Purchase #4	$107.53	9.327%	$117.5593	$117.56	$117.55	$117.60
Purchase #5	$178.37	7.164%	$191.1484	$191.15	$191.15	$191.10
Purchase #6	$19.75	7.860%	$21.3024	$21.30	$21.30	$21.30
Purchase #7	$120.58	6.867%	$128.8602	$128.86	$128.85	$128.90
7 purchase totals =	$860.72		$928.1001	$928.10	$928.05	$928.10