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	$235.30	12.575%	$264.889	$264.89	$264.90	$264.90
Purchase #2	$119.60	10.710%	$132.4092	$132.41	$132.40	$132.40
Purchase #3	$74.54	9.262%	$81.4439	$81.44	$81.45	$81.40
Purchase #4	$205.47	8.718%	$223.3829	$223.38	$223.40	$223.40
Purchase #5	$127.32	4.678%	$133.276	$133.28	$133.30	$133.30
Purchase #6	$64.75	12.328%	$72.7324	$72.73	$72.75	$72.70
Purchase #7	$19.25	3.586%	$19.9403	$19.94	$19.95	$19.90
7 purchase totals =	$846.23		$928.0737	$928.07	$928.15	$928.00