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	$24.69	11.267%	$27.4718	$27.47	$27.45	$27.50
Purchase #2	$193.62	6.146%	$205.5199	$205.52	$205.50	$205.50
Purchase #3	$228.33	11.756%	$255.1725	$255.17	$255.15	$255.20
Purchase #4	$18.37	4.460%	$19.1893	$19.19	$19.20	$19.20
Purchase #5	$111.69	10.371%	$123.2734	$123.27	$123.25	$123.30
Purchase #6	$179.32	9.543%	$196.4325	$196.43	$196.45	$196.40
Purchase #7	$46.78	13.843%	$53.2558	$53.26	$53.25	$53.30
7 purchase totals =	$802.80		$880.3152	$880.31	$880.25	$880.40